Create GH action to create tagged docker image on release

Every time we do a release we should create a corresponding docker image with the same tag (possibly replacing any instances of `+` with `-`). 

[Trigger](https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#release)
[Tag Name](https://stackoverflow.com/questions/63932728/github-action-release-tag)