TF-1311: set subscribeMailbox in UseCase and implement in Repository

lib/features/mailbox/domain/state/subscribe_mailbox_state.dart

@@ -0,0 +1,22 @@
+import 'package:core/core.dart';
+
+class LoadingSubscribeMailbox extends UIState {}
+
+class SubscribeMailboxSuccess extends UIState {
+
+  final bool subscribeMailbox;
+
+  SubscribeMailboxSuccess(this.subscribeMailbox);
+
+  @override
+  List<Object?> get props => [subscribeMailbox];
+}
+
+class SubscribeMailboxFailure extends FeatureFailure {
+  final dynamic exception;
+
+  SubscribeMailboxFailure(this.exception);
+
+  @override
+  List<Object> get props => [exception];
+}