createDocument method
Creates a document in the specified collection
Implementation
@override
Future<String> createDocument(String collection, Map<String, dynamic> data) async {
final coll = _collection(collection);
final id = _extractId(data) ?? _generateId();
final payload = _sanitizePayload(data);
payload['_id'] = id;
await coll.insertOne(payload);
return id;
}