chore(oauth2): enable user impersonation by default

[betodealmeida]

SUMMARY

When configuring a database, if the user provides OAuth2 client information (ID and secret) then we should automatically enable user impersonation for them.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

WIP

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

[villebro]

Is user impersonation really needed for OAuth? I would have assumed OAuth mostly makes user impersonation redundant, as you already have full user-specific authentication in place (no need for a service account).