Add support for publishing from an action for GitHub Pages

[OakLoaf]

It would be awesome if this action could have an option to provide support for the following publishing source in GitHub pages: https://docs.github.com/en/pages/getting-started-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site#publishing-with-a-custom-github-actions-workflow

[geoffreymcgill]

I am investigating getting Retype added to the list of publishing sources but it might not be possible. On first review, it appears GitHub has closed the process to getting accepted. We have applied to become a technology partner and will have to wait for that process to finalize.

We're also working on some other ideas for simplifying the publishing of Retype projects with GitHub Pages and other services.