Auto-review when assigned as reviewer

[dgershman]

Summary

Automatically start a review session when the user is assigned as a reviewer on a PR, with per-project opt-in.

Details

• Add a setting for a CSV list of projects to enable auto-review on (opt-in per project)
• When a review request is detected for an enabled project, automatically kick off the review process
• Should integrate with the existing notification/event system for review assignments