TF-2188 Add Canceled sending state

(cherry picked from commit fb802e50dbdeaddabf09f450ad19a75ed7d27f39)

lib/features/sending_queue/domain/model/sending_email.dart

@@ -105,6 +105,8 @@ class SendingEmail with EquatableMixin {
 
   bool get isSuccess => sendingState == SendingState.success;
 
+  bool get isCanceled => sendingState == SendingState.canceled;
+
   @override
   List<Object?> get props => [
     sendingId,