Migrate old Sage release tours and changelogs from Sage website and wiki to GitHub Releases or Sage documentation #31533
Description
Following the practices of many other projects, we make old release notes (release tours; but not changelogs) part of the normal documentation available on the GitHub Releases.
This is one more step to getting rid of the wiki.
Related: #31415 GH Actions workflow that deploys built documentation
CC: @slel
Component: documentation
Issue created by migration from https://trac.sagemath.org/ticket/31533