The publish stage has been split into two pieces - a draft step that
creates a draft version release in Github and a publish step that
publishes the draft, updates `latest_release` and pushes images to
DockerHub.
It is also possible to specify `--pre-release` to draft. Once published
such a release will be marked with a prominent warning in GitHub;
additionally we do not update `latest_release` in GitHub nor push an
update to the `latest` tag in DockerHub.
Adam Harrison
b13baccbd2