Add release notes for Review Board 5.0 beta 2.
Review Request #62 — Created Sept. 9, 2022 and updated
This release focuses on enhanced API tokens, repository ACL APIs (which will be backported to 4.0), some performance improvements, and other bug fixes. THis change adds the release notes, future-proofs some Sphinx configuration and references for 5.x releases, and tweaks the docs on the `invalidate-api-tokens` management command to let us link and to show the version in which this was added. Testing Done: Built the release notes. Checked for build errors, bad links, and spelling errors. Reviewed at https://reviews.reviewboard.org/r/12542/