TF-4356 Add filter event mail in search (#4357)

* Add `Events` filter checkbox in Advanced Search form
* Perform search email by `Events` filter in Advanced Search form
* Add `Event` quick search button in Search view
* Use `keywords` replace to `headers` for search event filter

lib/main/localizations/app_localizations.dart

@@ -5776,4 +5776,11 @@ class AppLocalizations {
       name: 'labelDescriptionHintText',
     );
   }
+
+  String get events {
+    return Intl.message(
+      'Events',
+      name: 'events',
+    );
+  }
 }