Release rules_docker on tag to the repo

[gravypod]

Right now releases are done manually be me from a script in google3 which has been deleted at head. This script zips the repo, generates a description, and uploads it to github. I would love if this process was automated outside of google3.

Ideal workflow:

1. We make a release branch git checkout -b release-0.29.0
2. We push the release branch git push -u origin release-0.29.0
3. Git automatically creates a release for this branch called 0.29.0.zip with all of the PRs that have been merged included in it.

[kriscfoster]

Hi @gravypod, PR listed above. I actually made the experience the following:

• go to whatever branch you want to release from e.g. master
• git tag -a v0.25.0 -m ""
• git push origin v0.25.0
• a release is created

Here's a demo.

[uhthomas]

Fixed by #2106