feat: Exposing Spanner client in dbapi connection (#1100)

* feat: Exposing Spanner client in dbapi connection

* Update comment

Co-authored-by: Knut Olav Løite <[email protected]>

---------

Co-authored-by: Knut Olav Løite <[email protected]>

Author: ankiaga

google/cloud/spanner_dbapi/connection.py

@@ -117,6 +117,13 @@ def __init__(self, instance, database=None, read_only=False):
         self._batch_dml_executor: BatchDmlExecutor = None
         self._transaction_helper = TransactionRetryHelper(self)
 
+    @property
+    def spanner_client(self):
+        """Client for interacting with Cloud Spanner API. This property exposes
+        the spanner client so that underlying methods can be accessed.
+        """
+        return self._instance._client
+
     @property
     def autocommit(self):
         """Autocommit mode flag for this connection.