[gh-pages] restrain repository size growth

[Shastick]

Every commit to master results in a new build of the website, which gets pushed to the gh-pages.

A single build of the website is pretty heavy (several hundreds of Mb, according to @barroco).

As a result, the size of the repository quickly grows, which might slowly become a hassle and a potential barrier to contributions.

This issue is here to discuss possible approaches.

Note: a repository with only the main branch and its entire history weights about ~23M

Options

• as a first fix, we may simply delete the history on the gh-pages branch
• updating the website with each commit is a feature we want to likely keep. We could chose to drop the history on that branch, always ensuring it has a single commit
• if keeping the history of the website is important, we could push it to a separate repository

Other option proposals are welcome.

Current plan

• (Possibly don't do this) fork the monitoring repo into the interuss organization, call it "monitoring-gh-pages-archive", only keep the gh-pages branch.
• on monitoring, in the relevant github action:
  • (Possibly don't do this) push updates to the gh-pages branch to the archive repo rather than monitoring
  • force-push a single commit containing the current version of the website to the gh-pages branch on the monitoring repo