feat(dependencies): add searchable fields to headline, topic, and source clients

- Added 'title' as a searchable field for headlines
- Added 'name' as a searchable field for topics and sources

Author: fulleni

lib/src/config/app_dependencies.dart

@@ -94,20 +94,23 @@ class AppDependencies {
         modelName: 'headlines',
         fromJson: Headline.fromJson,
         toJson: (item) => item.toJson(),
+        searchableFields: ['title'],
         logger: Logger('HtDataMongodb<Headline>'),
       );
       final topicClient = HtDataMongodb<Topic>(
         connectionManager: _mongoDbConnectionManager,
         modelName: 'topics',
         fromJson: Topic.fromJson,
         toJson: (item) => item.toJson(),
+        searchableFields: ['name'],
         logger: Logger('HtDataMongodb<Topic>'),
       );
       final sourceClient = HtDataMongodb<Source>(
         connectionManager: _mongoDbConnectionManager,
         modelName: 'sources',
         fromJson: Source.fromJson,
         toJson: (item) => item.toJson(),
+        searchableFields: ['name'],
         logger: Logger('HtDataMongodb<Source>'),
       );
       final countryClient = HtDataMongodb<Country>(