Archive old LTS changelogs

[timja]

Describe your use-case which is not covered by existing documentation.

We should limit the https://www.jenkins.io/changelog-stable/ page to displaying only the last 2 years of changelogs.

Older changelogs should be viewable on a separate archive page.
Ideally this is automated in Ruby code. Weekly releases already have something that makes it only show the last 30 releases or so.

This will also fix that releases older than 2.19.4 (8 years old) have different styling because its a direct html file thats included.

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

#7479 (comment)

Are you interested in contributing a fix?

Not right now, but maybe @janfaracik?