Add a pom.xml for org.eclipse.paho.sample.mqttv3app sample to make it maven compliant

[stutiuneyal]

Problem Summary

Currently the org.eclipse.paho.sample.mqttv3app sample is not maven compliant i.e. doesn't have a project level pom.xml file, because of which if we are to use a specific sample file, we need to clone that specific file, edit the package, compile it and then run the sample.

Adding a project level pom.xml file will help us to compile the entire sample, install its dependencies and package it as a jar which then we can directly run.

Tasks

• Create a project level pom.xml file, including all the dependencies and plugins
• Create a new Main.java file which will act as an entry point for our pom.xml
• Since we are having 3 java samples inside our org.eclipse.paho.sample.mqttv3app package, so we need to add arguments in our Main.java file so when we run our project jar, using these args we can run any sample that we want inside the package.
• Create a Readme.md file elaborating the instructions on how to build and run the sample.