docs(data_mongodb): add reference link for 'language' field conflict

- Include a link to MongoDB community forum discussion about the 'language' field conflict
- Improve documentation by providing a reference for the field renaming workaround

Author: fulleni

lib/src/data_mongodb.dart

@@ -90,7 +90,7 @@ class DataMongodb<T> implements DataClient<T> {
   /// conflicts with a reserved keyword in MongoDB's `text` search options.
   /// To prevent this, it transparently renames any 'language' field to
   /// 'modelLanguage' before the document is written.
-  /// 
+  ///
   /// https://www.mongodb.com/community/forums/t/just-to-point-out-do-not-name-a-field-language-if-you-are-planning-to-create-an-index/263793
   Map<String, dynamic> _transformMapForDb(Map<String, dynamic> map) {
     if (map.containsKey('language')) {