Migrate off github actions ported build system to pure circleci and cache installed dependencies

[nelsonjchen]

Sometimes it errors out for no reason every hour, sending build error messages out. We should migrate off and change CircleCI to cache the dependencies so there's less risk of reaching out to a PyPI that is down.

In the meantime, I've extracted the GitHub Pelican Build Action and put it out there. It's not suitable for us but at least it might be useful for other Pelican users.