TF-4301 Add E2E tests for label creation and tagging from email view

lib/features/thread_detail/presentation/extension/labels/add_label_to_thread_extension.dart

@@ -1,4 +1,5 @@
 import 'package:dartz/dartz.dart';
+import 'package:flutter/material.dart';
 import 'package:jmap_dart_client/jmap/account_id.dart';
 import 'package:jmap_dart_client/jmap/core/session/session.dart';
 import 'package:jmap_dart_client/jmap/mail/email/email.dart';
@@ -32,6 +33,7 @@ extension AddLabelToThreadExtension on ThreadDetailController {
 
     final newLabel = await DialogRouter().openDialogModal(
       child: AddLabelToEmailModal(
+        key: const Key('add_label_to_thread_modal'),
         labels: labels,
         emailLabels: threadLabels,
         emailIds: emailIds,