New Features
* feat(firestore): Upgrade `google-cloud-firestore` to support Firestore Multi Database (827)
* feat: Support passing `google.auth` typed credentials in `initialize_app()` (821)
* feat(firestore): Add Firestore Multi Database Support (818)
Miscellaneous
* [chore] Release 6.6.0 Take 2 (830)
* [chore] Release 6.6.0 (829)
* chore: Add `X-Goog-Api-Client` metric header to requests (826)
* chore: Create dependabot.yml (820)
* [chore] Bump cachecontrol (819)
* chore: Update `actions/upload-artifact` (812)
* chore(deps): bump actions/download-artifact in /.github/workflows (810)
* chore: Remove Python 3.7 from workflows (806)
* Fix link to `requests.Response` in FirebaseError. (800)
* chore: Update integration test resources (796)