Update various dependencies

[derekherman]

Summary

Updates Lighthouse to v8.1.0 and PHPCompatibilityWP to v2.1.2 and installs Chromium v91.0.4472.164-r0 in the Docker image. Additionally, this changes the Firestore database rules to be explicit about what is allowed.

This branch replaces all open PR's.

Checklist

• [x] My code is tested and passes existing tests.
• [x] My code follows the Tide Contributing Guide (updates are often made to the guidelines, check it out periodically).