TF-3449 Add integration test for send email with mark as important

Signed-off-by: dab246 <tdvu@linagora.com>

lib/features/composer/presentation/composer_view.dart

@@ -500,6 +500,7 @@ class ComposerView extends GetWidget<ComposerController> {
       PopupMenuItem(
         padding: EdgeInsets.zero,
         child: PopupItemWidget(
+          key: const Key('mark_as_important_popup_item'),
           iconAction: controller.imagePaths.icMarkAsImportant,
           nameAction: AppLocalizations.of(context).markAsImportant,
           styleName: ComposerStyle.popupItemTextStyle,

lib/features/composer/presentation/widgets/mobile/app_bar_composer_widget.dart

@@ -91,6 +91,7 @@ class AppBarComposerWidget extends StatelessWidget {
           ),
           const SizedBox(width: MobileAppBarComposerWidgetStyle.space),
           TMailButtonWidget.fromIcon(
+            key: const Key('composer_more_button'),
             icon: imagePaths.icMore,
             iconColor: MobileAppBarComposerWidgetStyle.iconColor,
             backgroundColor: Colors.transparent,

lib/features/thread/presentation/mixin/base_email_item_tile.dart

@@ -357,6 +357,7 @@ mixin BaseEmailItemTile {
 
   Widget buildMarkAsImportantIcon(BuildContext context) {
     return Padding(
+      key: const Key('important_flag_icon'),
       padding: ItemEmailTileStyles.getSpaceCalendarEventIcon(
         context,
         responsiveUtils,