Add ability for users to pass external query to do minimal transformation on data in https://github.com/GoogleCloudPlatform/dataproc-templates/blob/main/python/dataproc_templates/gcs/gcs_to_bigquery.py The feature is similar to https://github.com/GoogleCloudPlatform/dataproc-templates/blob/4dd07897bf830f2b70bf3ad0dca13ac5f46a9548/python/dataproc_templates/gcs/gcs_to_gcs.py#L167