Added method for getting channel key or conversation ID

[AbhijeetRanjan308]

Summary

• Added a method to get channel key if you pass conversation ID or conversation ID if you pass channel key

Function

/// Just need to pass either 'clientChannelKey' or 'channelID' 
dynamic objc = {'clientChannelKey': 'pKC6riItFm7eMmogrJ2gz3LvjrD9nwaU', 'channelID': 95713948}   

KommunicateFlutterPlugin.getConversarionIdOrKey(objc).then((value) {
                     print('User Channel id : $value');
                    }
                  ).catchError((error) {
                      print('Error in channel user details : ' +
                          error.toString());
                    });