[CM-1119] - add support for Events - Android

[amntoppo]

Issue:

• To use events, customers had to use Native Android and iOS Code.
• We have added the support to listen to events directly in Flutter.

How to implement?

• In Dart code, we need to create a Method Channel - "kommunicate_flutter"
• This will give us setMethodCallHandler which returns all the events which we send from Native code.

Sample Code:

MethodChannel channel = MethodChannel('kommunicate_flutter');

channel.setMethodCallHandler((call){
      if(call.method == 'onPluginLaunch'){
        print(call.arguments);
      } else if(call.method == 'onPluginDismiss'){
        print(call.arguments);
      } else if(call.method == 'onConversationResolved'){
        print(call.arguments);
      } else if(call.method == 'onConversationRestarted'){
        print(call.arguments);
      } else if(call.method == 'onRichMessageButtonClick'){
        print(call.arguments);
      } else if(call.method == 'onStartNewConversation'){
        print(call.arguments);
      } else if(call.method == 'onMessageSent'){
        print(call.arguments);
      } 

      return null;
    });

-- This PR is for Android events only. Will be creating a separate PR for IOS events.