This begins providing release notes for changes and provides scripts to
facilitate this:
- tools/mkrelease will update RELEASES.md and run some checks.
- build-aux/release-check is intended for use in pipelines (e.g. see
.gitlab-ci.yml) to verify that releases were done properly.
We moved to an internal container registry so that we do not have to rely on
DockerHub. Since TAME is a public project, this will allow our
configuration internally to vary from a public configuration.