TF-3082 Warn user and save identity cache on reload/session expired

lib/features/identity_creator/data/datasource/identity_creator_data_source.dart

@@ -0,0 +1,10 @@
+import 'package:jmap_dart_client/jmap/account_id.dart';
+import 'package:jmap_dart_client/jmap/core/user_name.dart';
+import 'package:tmail_ui_user/features/identity_creator/domain/model/identity_cache.dart';
+
+abstract class IdentityCreatorDataSource {
+  Future<void> saveIdentityCacheOnWeb(
+    AccountId accountId,
+    UserName userName,
+    {required IdentityCache identityCache});
+}