TF-831: implement Add a new recipient in forwarding

lib/features/manage_account/domain/model/add_recipients_in_forwarding_request.dart

@@ -0,0 +1,23 @@
+import 'package:equatable/equatable.dart';
+import 'package:forward/forward/tmail_forward.dart';
+
+class AddRecipientInForwardingRequest with EquatableMixin {
+  final TMailForward currentForward;
+  final Set<String> listRecipientAdded;
+
+  AddRecipientInForwardingRequest({
+    required this.currentForward,
+    required this.listRecipientAdded,
+  });
+
+  TMailForward get newTMailForward {
+    final newListRecipients = currentForward.forwards
+        .where((recipient) => !listRecipientAdded.contains(recipient))
+        .toSet();
+    newListRecipients.addAll(listRecipientAdded);
+    return currentForward.copyWith(forwards: newListRecipients);
+  }
+
+  @override
+  List<Object?> get props => [currentForward, listRecipientAdded];
+}