Include GitHub Actions workflows in package template

[namurphy]

GitHub Actions has been gaining a lot of traction, so it would be really helpful for the package template to already have configuration files for GitHub Actions built-in. That would simplify the process of setting up continuous integration testing for people who end up using the template for a project that ends up being hosted on ye olde GitHub.

Since there's a chance that some projects would end up being hosted on GitLab or elsewhere, it might be good to ask if the user wants to have these configuration files automagically included or not.

I'm also wondering if setting up GitHub Actions in the template would help allow the template itself to be (meta?)tested with GitHub Actions, but that's outside the scope of this particular issue.

[Cadair]

I'm also wondering if setting up GitHub Actions in the template would help allow the template itself to be (meta?)tested with GitHub Actions, but that's outside the scope of this particular issue.

We already do run tests of the template with GitHub actions.

I definitely think that this repo is the right place to provide an example of using https://github.com/OpenAstronomy/github-actions-workflows/ but I will be making it opt-in.