[FEAT] Kotlin convert

[yatharthranjan]

Is your feature request related to a problem? Please describe.
Java code is comprehensive and hard to maintain.

Describe the solution you'd like
Now that the xmpp code is removed, we can convert the code to kotlin in steps.

Describe alternatives you've considered
N/A

Priority
3

Difficulty
7

Additional context
We can do this in steps and the intermediate stages can contain both java and kotlin code. We can start with the org.radarbase.fcm package.