docs: add notice not to use gevent worker with bigquery datasource

[okayhooni]

SUMMARY

• Currently, Google BigQuery python sdk is not compatible with gevent, due to some dynamic monkeypatching on python core library by gevent.
  • to_dataframe function is blocked when gunicorn is run with worker class gevent googleapis/python-bigquery#697
  • Python Bigquery to_dataframe function is blocked when gunicorn is run with worker class gevent gevent/gevent#1797
  • gevent compatibility grpc/grpc#4629
• Even though enabling GLOBAL_ASYNC_QUERIES feature flag, some superset UI&API remain to be called on webserver, instead of celery worker. (ex: force_refresh UI on v2.1.0)
• So, it helps superset users, to notice gunicorn with gevent worker type is not compatible with bigquery data source.
• Related community links
  • Unable to query BigQuery data - queries executed successful at BigQuery but results not returned at Superset #23979
  • https://apache-superset.slack.com/archives/C015WAZL0KH/p1686908792979199

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

• just docs update

TESTING INSTRUCTIONS

• just docs update

ADDITIONAL INFORMATION

• Has associated issue: Unable to query BigQuery data - queries executed successful at BigQuery but results not returned at Superset #23979
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[michael-s-molina]

Thanks for the docs @okayhooni!