feat(content_management): add data update handler for headline creation

- Implement CreateHeadlineDataUpdated event handling in CreateHeadlineBloc
- Update state with new country data when CreateHeadlineDataUpdated event is triggered

Author: fulleni

lib/content_management/bloc/create_headline/create_headline_bloc.dart

@@ -31,6 +31,7 @@ class CreateHeadlineBloc
     on<CreateHeadlineCountryChanged>(_onCountryChanged);
     on<CreateHeadlineStatusChanged>(_onStatusChanged);
     on<CreateHeadlineSubmitted>(_onSubmitted);
+    on<CreateHeadlineDataUpdated>(_onDataUpdated);
   }
 
   final DataRepository<Headline> _headlinesRepository;
@@ -180,4 +181,11 @@ class CreateHeadlineBloc
       );
     }
   }
+
+  void _onDataUpdated(
+    CreateHeadlineDataUpdated event,
+    Emitter<CreateHeadlineState> emit,
+  ) {
+    emit(state.copyWith(countries: event.countries));
+  }
 }