TF-3563 Add integration test for case download attachment in EmailView

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

integration_test/tests/email_detailed/export_attachment_test.dart

@@ -0,0 +1,9 @@
+import '../../base/test_base.dart';
+import '../../scenarios/email_detailed/export_attachment_scenario.dart';
+
+void main() {
+  TestBase().runPatrolTest(
+    description: 'Should auto preview attachment when export attachment successfully',
+    scenarioBuilder: ($) => ExportAttachmentScenario($),
+  );
+}