TF-1204 Add FirebaseRegistration/get method/response and write unit test

fcm/lib/utils/fcm_utils.dart

@@ -1,6 +0,0 @@
-
-import 'package:jmap_dart_client/jmap/core/capability/capability_identifier.dart';
-
-class FCMUtils {
-  static final capabilityFCM = CapabilityIdentifier(Uri.parse('com:linagora:params:jmap:firebase:push'));
-}

fcm/lib/utils/firebase_utils.dart

@@ -0,0 +1,6 @@
+
+import 'package:jmap_dart_client/jmap/core/capability/capability_identifier.dart';
+
+class FirebaseUtils {
+  static final capabilityLinagoraFirebase = CapabilityIdentifier(Uri.parse('com:linagora:params:jmap:firebase:push'));
+}