Add BigQuery connector beta banner

doc/developer-center/import-api/guides/07-database-connectors.md

@@ -1083,7 +1083,9 @@ When using database connectors, the following limitations or restrictions are en
 
 **Note:** The number of imported columns will affect the performance of the connector.
 
-### The BigQuery Connector
+### The BigQuery Connector (beta)
+
+:warning: This connector is in **beta** stage and the API might change or have limited support :warning:
 
 The BigQuery Connector allows you to import data into a CARTO account as tables from BigQuery. Note that **this connector is disabled by default** in the CARTO importer options. If you are interested in enabling it, [contact us](mailto:sales@carto.com) for details.
 
@@ -1295,4 +1297,4 @@ from_external_source | Has the value **false** for all connector-based synchroni
   "from_external_source":false
   }
 }
-```
+```