Add link checking github action

[JackWilb]

Adds link checking with html proofer

TODO:

• [x] Refine the options we're using so we don't get so many false positives
• [x] See why some links are marked as invalid (seems that they redirect and not always to the right place)
• [x] Consider removing image alt text check (or image check altogether)
• [x] Add user agent and cookies file to allow dx.doi.org redirects to work
• [x] Remove the on push trigger (We've decided that we do want on push)
• [x] Change the time it runs from 00:00 UTC to a different time that makes sense, maybe early morning for us (06:00/07:00 Mountain)
• [x] Add ability to ignore certain links that are known true, but don't resolve

[alexsb]

I should have resolved all errors that can be resolved at this point. For the rest of the links that throw an error, it would be good to either ignore the error, or create an exception with a warning that doesn't prevent merging.