feat(content_management): add event to reset filter dialog selections

- Introduce FilterDialogReset event to reset all temporary filter selections
- This enhancement allows users to easily revert filter changes back to their initial state

Author: fulleni

lib/content_management/widgets/filter_dialog/bloc/filter_dialog_event.dart

@@ -116,3 +116,9 @@ final class FilterDialogHeadquartersCountryIdsChanged
   @override
   List<Object?> get props => [countryIds];
 }
+
+/// Event to reset all temporary filter selections in the dialog to their
+/// initial state.
+final class FilterDialogReset extends FilterDialogEvent {
+  const FilterDialogReset();
+}