Release docs action

[dopplershift]

Right now, docs are only built on merge, not on release. This makes it impossible to build docs for a new version series on release.

Also need to handle updating the version json.

[akrherz]

I also notice that dev docs are getting deployed twice, once for 3.8 Requirements and again for 3.9 Requirements. See commit history. I am currently attempting to resolve why docs won't cleanly build in my fork, so am reviewing the current actions.

[dopplershift]

Yeah, for some reason, that I don't understand now, I didn't make the deploy key on Python 3.9.

[dopplershift]

Taken care of by #1836 and #1837.