Fixes https://github.com/certbot/certbot/issues/8171.
See the comment at the top of the script to learn how to set things up and run this. Running the script between releases will have no effect on our snaps and it should fail when creating the GitHub release. The latter is described at https://github.com/certbot/certbot/pull/8189#discussion_r466707114.
* Rename create_github_release to finish_release
* Add initial version of snap release automation.
* Handle snapcraft login.
* Catch OSError raised when snapcraft doesn't exist.
* Update documentation.
* Only publish the Certbot snap for now.
* Fix typo.
* Document other exceptions.
* Document assertion
* Add status message before getting revisions.
* Publish all snaps.
