Push container images to GitHub Container Registry

`aswfdocker` should be able to push container images to both Docker Hub and [GitHub Container Registry](https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry)

No files or tests are named. Start by locating the existing Docker Hub image-publishing entry point and its configuration, then determine how the same images should be published to GitHub Container Registry. Done means both registries receive the intended container images and the relevant workflow checks pass.

Written by the indexing model from the issue text.