feat(data_mongodb): add pre-insertion document logging

This change enhances the diagnostic capabilities of the DataMongodb class
by logging the document to be inserted right before executing the insertOne
operation. This will help in debugging and verifying the data being sent
to the database.

Author: fulleni

lib/src/data_mongodb.dart

@@ -288,6 +288,9 @@ class DataMongodb<T> implements DataClient<T> {
       final doc = _prepareDocumentForInsertionOrUpdate(item);
       _logger.finer('Prepared document for insertion with _id: ${doc['_id']}');
 
+      // DIAGNOSTIC: Log the exact document before insertion.
+      _logger.info('Executing insertOne with document: $doc');
+
       final writeResult = await _collection.insertOne(doc);
 
       if (!writeResult.isSuccess) {