Add github.com/eclipse/paho.mqtt.golang

This dependency is required to use MQTT with Go.

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+
+[![PkgGoDev](https://pkg.go.dev/badge/github.com/eclipse/paho.mqtt.golang)](https://pkg.go.dev/github.com/eclipse/paho.mqtt.golang)
+[![Go Report Card](https://goreportcard.com/badge/github.com/eclipse/paho.mqtt.golang)](https://goreportcard.com/report/github.com/eclipse/paho.mqtt.golang)
+
+Eclipse Paho MQTT Go client
+===========================
+
+
+This repository contains the source code for the [Eclipse Paho](https://eclipse.org/paho) MQTT 3.1/3.11 Go client library. 
+
+This code builds a library which enable applications to connect to an [MQTT](https://mqtt.org) broker to publish 
+messages, and to subscribe to topics and receive published messages.
+
+This library supports a fully asynchronous mode of operation.
+
+A client supporting MQTT V5 is [also available](https://github.com/eclipse/paho.golang).
+
+Installation and Build
+----------------------
+
+The process depends upon whether you are using [modules](https://golang.org/ref/mod) (recommended) or `GOPATH`. 
+
+#### Modules
+
+If you are using [modules](https://blog.golang.org/using-go-modules) then `import "github.com/eclipse/paho.mqtt.golang"` 
+and start using it. The necessary packages will be download automatically when you run `go build`. 
+
+Note that the latest release will be downloaded and changes may have been made since the release. If you have 
+encountered an issue, or wish to try the latest code for another reason, then run 
+`go get github.com/eclipse/paho.mqtt.golang@master` to get the latest commit.
+
+#### GOPATH
+
+Installation is as easy as:
+
+```
+go get github.com/eclipse/paho.mqtt.golang
+```
+
+The client depends on Google's [proxy](https://godoc.org/golang.org/x/net/proxy) package and the 
+[websockets](https://godoc.org/github.com/gorilla/websocket) package, also easily installed with the commands:
+
+```
+go get github.com/gorilla/websocket
+go get golang.org/x/net/proxy
+```
+
+
+Usage and API
+-------------
+
+Detailed API documentation is available by using to godoc tool, or can be browsed online
+using the [pkg.go.dev](https://pkg.go.dev/github.com/eclipse/paho.mqtt.golang) service.
+
+Samples are available in the `cmd` directory for reference.
+
+Note:
+
+The library also supports using MQTT over websockets by using the `ws://` (unsecure) or `wss://` (secure) prefix in the
+URI. If the client is running behind a corporate http/https proxy then the following environment variables `HTTP_PROXY`,
+`HTTPS_PROXY` and `NO_PROXY` are taken into account when establishing the connection.
+
+Troubleshooting
+---------------
+
+If you are new to MQTT and your application is not working as expected reviewing the
+[MQTT specification](https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html), which this library implements,
+is a good first step. [MQTT.org](https://mqtt.org) has some [good resources](https://mqtt.org/getting-started/) that answer many 
+common questions.
+
+### Error Handling
+
+The asynchronous nature of this library makes it easy to forget to check for errors. Consider using a go routine to 
+log these: 
+
+```go
+t := client.Publish("topic", qos, retained, msg)
+go func() {
+    _ = t.Wait() // Can also use '<-t.Done()' in releases > 1.2.0
+    if t.Error() != nil {
+        log.Error(t.Error()) // Use your preferred logging technique (or just fmt.Printf)
+    }
+}()
+```
+
+### Logging
+
+If you are encountering issues then enabling logging, both within this library and on your broker, is a good way to
+begin troubleshooting. This library can produce various levels of log by assigning the logging endpoints, ERROR, 
+CRITICAL, WARN and DEBUG. For example:
+
+```go
+func main() {
+	mqtt.ERROR = log.New(os.Stdout, "[ERROR] ", 0)
+	mqtt.CRITICAL = log.New(os.Stdout, "[CRIT] ", 0)
+	mqtt.WARN = log.New(os.Stdout, "[WARN]  ", 0)
+	mqtt.DEBUG = log.New(os.Stdout, "[DEBUG] ", 0)
+
+	// Connect, Subscribe, Publish etc..
+}
+```
+
+### Common Problems
+
+* Seemingly random disconnections may be caused by another client connecting to the broker with the same client 
+identifier; this is as per the [spec](https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc384800405).
+* Unless ordered delivery of messages is essential (and you have configured your broker to support this e.g. 
+  `max_inflight_messages=1` in mosquitto) then set `ClientOptions.SetOrderMatters(false)`. Doing so will avoid the 
+  below issue (deadlocks due to blocking message handlers).
+* A `MessageHandler` (called when a new message is received) must not block (unless 
+  `ClientOptions.SetOrderMatters(false)` set). If you wish to perform a long-running task, or publish a message, then 
+  please use a go routine (blocking in the handler is a common cause of unexpected `pingresp 
+not received, disconnecting` errors). 
+* When QOS1+ subscriptions have been created previously and you connect with `CleanSession` set to false it is possible 
+that the broker will deliver retained messages before `Subscribe` can be called. To process these messages either 
+configure a handler with `AddRoute` or set a `DefaultPublishHandler`. If there is no handler (or `DefaultPublishHandler`) 
+then inbound messages will not be acknowledged. Adding a handler (even if it's  `opts.SetDefaultPublishHandler(func(mqtt.Client, mqtt.Message) {})`) 
+is highly recommended to avoid inadvertently hitting inflight message limits.
+* Loss of network connectivity may not be detected immediately. If this is an issue then consider setting 
+`ClientOptions.KeepAlive` (sends regular messages to check the link is active).
+* Reusing a `Client` is not completely safe. After calling `Disconnect` please create a new Client (`NewClient()`) rather 
+than attempting to reuse the existing one (note that features such as `SetAutoReconnect` mean this is rarely necessary).
+* Brokers offer many configuration options; some settings may lead to unexpected results.
+* Publish tokens will complete if the connection is lost and re-established using the default
+options.SetAutoReconnect(true) functionality (token.Error() will return nil). Attempts will be made to re-deliver the
+message but there is currently no easy way know when such messages are delivered.
+
+If using Mosquitto then there are a range of fairly common issues:
+* `listener` - By default [Mosquitto v2+](https://mosquitto.org/documentation/migrating-to-2-0/) listens on loopback 
+interfaces only (meaning it will only accept connections made from the computer its running on).
+* `max_inflight_messages` - Unless this is set to 1 mosquitto does not guarantee ordered delivery of messages. 
+* `max_queued_messages` / `max_queued_bytes` - These impose limits on the number/size of queued messages. The defaults
+may lead to messages being silently dropped.
+* `persistence` - Defaults to false (messages will not survive a broker restart)
+* `max_keepalive` - defaults to 65535 and, from version 2.0.12, `SetKeepAlive(0)` will result in a rejected connection 
+by default.
+
+Reporting bugs
+--------------
+
+Please report bugs by raising issues for this project in github https://github.com/eclipse/paho.mqtt.golang/issues
+
+A limited number of contributors monitor the issues section so if you have a general question please see the 
+resources in the [more information](#more-information) section for help.
+
+We welcome bug reports, but it is important they are actionable. A significant percentage of issues reported are not 
+resolved due to a lack of information. If we cannot replicate the problem then it is unlikely we will be able to fix it. 
+The information required will vary from issue to issue but almost all bug reports would be expected to include: 
+
+* Which version of the package you are using (tag or commit - this should be in your `go.mod` file)
+* A full, clear, description of the problem (detail what you are expecting vs what actually happens).
+* Configuration information (code showing how you connect, please include all references to `ClientOption`)
+* Broker details (name and version).
+
+If at all possible please also include:
+* Details of your attempts to resolve the issue (what have you tried, what worked, what did not).
+* A [Minimal, Reproducible Example](https://stackoverflow.com/help/minimal-reproducible-example). Providing an example
+is the best way to demonstrate the issue you are facing; it is important this includes all relevant information
+(including broker configuration). Docker (see `cmd/docker`) makes it relatively simple to provide a working end-to-end
+example.
+* Broker logs covering the period the issue occurred.
+* [Application Logs](#logging) covering the period the issue occurred. Unless you have isolated the root cause of the 
+issue please include a link to a full log (including data from well before the problem arose).
+
+It is important to remember that this library does not stand alone; it communicates with a broker and any issues you are 
+seeing may be due to:
+
+* Bugs in your code.
+* Bugs in this library.
+* The broker configuration.
+* Bugs in the broker.
+* Issues with whatever you are communicating with.
+
+When submitting an issue, please ensure that you provide sufficient details to enable us to eliminate causes outside of
+this library.
+
+Contributing
+------------
+
+We welcome pull requests but before your contribution can be accepted by the project, you need to create and 
+electronically sign the Eclipse Contributor Agreement (ECA) and sign off on the Eclipse Foundation Certificate of Origin.
+
+More information is available in the 
+[Eclipse Development Resources](http://wiki.eclipse.org/Development_Resources/Contributing_via_Git); please take special 
+note of the requirement that the commit record contain a "Signed-off-by" entry.
+
+More information
+----------------
+
+[Stack Overflow](https://stackoverflow.com/questions/tagged/mqtt+go) has a range questions/answers covering a range of 
+common issues (both relating to use of this library and MQTT in general). This is the best place to ask general questions 
+(including those relating to the use of this library).
+
+Discussion of the Paho clients takes place on the [Eclipse paho-dev mailing list](https://dev.eclipse.org/mailman/listinfo/paho-dev).
+
+General questions about the MQTT protocol are discussed in the [MQTT Google Group](https://groups.google.com/forum/?hl=en-US&fromgroups#!forum/mqtt).
+
+There is much more information available via the [MQTT community site](http://mqtt.org).