PEP 101: Remove three manual steps to edit python.org pages

[hugovk]

I added a https://python.org/downloads/latest/prerelease redirect (python/pythondotorg#2823) so RMs no longer need to manually edit https://www.python.org/download/pre-releases/ for every pre-release and .0 final.

I also changed https://www.python.org/doc/versions/ to be generated from the releases in the CMS (python/pythondotorg#2813), so it's no longer a static CMS page that RMs forget to manually edit for every non-pre-release.

(The old static one is at https://www.python.org/doc/versions-old/ for now, will unpublish later.)

Related release-tools PR: python/release-tools#308

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📚 Documentation preview 📚: https://pep-previews--4717.org.readthedocs.build/

[hugovk]

That first bullet point was essentially a duplicate of the fourth one!

• Add the new version to the “Python documentation by version” page and remove the current version from any ‘in development’ section.

• If appropriate, update the “Python documentation by version” page.
  This lists all releases of Python by version number and links to their static (not built daily) online documentation. There’s a link at the bottom to the in-development version. And yes you can press the shiny, exciting “Edit this page” button.

Removed as well!

[hugovk]

And that last manual step of the bunch removed, a "superseded by" note is automatically added: python/pythondotorg#2827