[Feature] Add Override query to GCS to BigQuery Template

[surjits254]

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

dataproc-templates/python/dataproc_templates/gcs/gcs_to_gcs.py

Line 167 in 4dd0789

if sql_query: