We currently have a version drop-down all the way to 0.11, which I think is rarely used or completely unused. Also when pushing commits to mne-tools.github.io repo I get warnings like this that suggest that our HTML has vulnerabilities, which is presumably due to ancient webpages:

remote: GitHub found 16 vulnerabilities on mne-tools/mne-tools.github.io's default branch (16 moderate). To find out more, visit:
remote:      https://github.com/mne-tools/mne-tools.github.io/security/dependabot

I suggest we put some lower bound on which versions to archive -- maybe the last 2 years worth of versions? This should help reduce this security issue, and also make the site faster to deploy and fetch, etc. If we don't want to get rid of the 0.11 docs entirely for example we could archive them in a .zip and link to them somewhere in our docs. This could easily be added as another step in our release process, and I don't think it would take too much extra time/effort (< 10 min) during release time.

Any objections? @drammock I'm releasing today but can take care of the changes this week and backport them to the maint/1.5 branch I'm going to make (so that links to the archived versions exist).