Add GitHub Action to check broken links in documentation.

[dalonsoa]

URLs often stop working as time goes by so having an automated way of monitoring for those and flagging them to be sorted is useful.

A handy GitHub Action to check broken links is readily available to be implemented checking MUSE documentation deployed in Read The Docs.

[dc2917]

I'll tackle this

[dalonsoa]

If the one running doesn't work, try this one: https://github.com/ruzickap/action-my-broken-link-checker

It will not create issues automatically for each broken link, but it will flag those broken and, importantly, you can have a higher degree of control of the depth of the links that are followed.

[dalonsoa]

Ok, it has finished and found 1 broken link - Anaconda, funny enough. It has not created the issue because issues were disabled for the repo, but it tried to.

So, what do you think - shall we use one or the other?