Move the upgrade notes and merge them with the releases pages
We have two places documenting the upgrades between releases. For example, for 6.0:
- https://docs.gitlab.com/charts/installation/upgrade.html#upgrade-to-version-60
- https://docs.gitlab.com/charts/releases/6_0.html
Also, I don't see a reason we only document the major releases in the release notes.
It would be a good idea to move the version-specific notes in the release notes. Much like we do with Omnibus, for example https://docs.gitlab.com/omnibus/update/gitlab_14_changes.html.