Final changes to release workflow to make submodule releases possible.

[aiuto]

• fix a lot of bugs in release_module.yaml and release_prep.sh
• Update the version.bzl file for the submodule when releasing. That's one less thing to be out of sync.
• Update pkg/releasing tools to allow for releases that are not strictly a version number.
  • Add a release_name concept, which is distinct from repo and version, so that we can form URLs like url = 'https://github.com/ORG/REPO/releases/download/SUBMODULE-VERSION/FILE_NAME'

This was used to create the release rules_pkg_providers-0.0.1g.
After this is committed, I'll delete that pre-release sample and do a real one.