Autogenerate documentation previews on pull requests in CI

Would be very useful to autogenerate documentation previews on pull requests in CI (e.g. like this done with readthedocs, https://dtool-lookup-gui--309.org.readthedocs.build/en/309/). I think this should be possible for gh-pages as well, maybe with the help of https://github.com/rossjrw/pr-preview-action.