Publish preview for open pull requests

[elf-pavlik]

It is commonly needed to have preview for pull requests. Action could be configured to use pr number and publish version from the PR in the sub path of GitHub pages. Even better if it would comment on PR with link to the preview and/or include link in the checks.

In the past we used netlify integration to automate it but doing it with gh actions and gh pages would be preferable.

[sidvishnoi]

See #194 (comment)

[elf-pavlik]

Thank you!