Move Nightly Library installs to GH Actions

[partouf]

This is still an admin cronjob, but is similar enough to nightly install of compilers that it can move to GH actions. This would make it a lot more transparent as to what's going right/wrong.

The question is if it reveals any secrets? and if so, what can we do about it

[partouf]

Also: how long does it take and would that time be acceptable to wait on before anyone can run a compiler discovery as it will take up the GH runner. Can we tell GH runner to accept 2 simultaneous workflows?