fix: OAuth2 in async DBs

[betodealmeida]

SUMMARY

When Superset triggers OAuth2 it needs to pass to the OAuth provider a redirect URL, to where the user will be sent with the initial OAuth2 code after granting access to Superset. This redirect URL is built using url_for, and needs to run in a Flask request context in order to have access to the application SERVER_NAME, in addition to PREFERRED_URL_SCHEME and APPLICATION_ROOT.

This PR modifies the get_sql_results Celery task to run the query under a dummy request context. This is enough for Superset to compute the redirect URL when the database is configured to run in async mode.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before:

After:

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• 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

[eschutho]

LGTM