Add release notes for Review Board 5.0.
Review Request #90 — Created Oct. 25, 2022 and updated
This is a large release, moving onto modern architecture, and introducing many new features for reviewers and administrators. This includes Stale Ship-It! indicators, Trojan Source detection, Single Sign-On, and more. This change adds release notes covering all the public changes we want to advertise for the release. This lacks screenshots, but the plan is to add them in a follow-up change. Testing Done: Built the release notes. Checked for spelling errors, bad links, and build errors. Reviewed at https://reviews.reviewboard.org/r/12660/