Preview docs as part of PR

[stefmolin]

As part of the GitHub Actions workflows that run when a PR is opened, I'd like to have something like Matplotlib has that makes it possible to preview the built docs without downloading an artifact or building the docs locally.

Numpydoc also has this:

The details link goes to a preview hosted on CircleCI, but maybe a GitHub-only solution is possible with the latest changes in the artifact action, and using this action to set the details URL?

Read the docs PR previews could also be an option.