Drop Docker Hub and only use GH Container Repository

[jsf9k]

💡 Summary

We should consider dropping the cisagov Docker Hub organization in favor of GitHub Container Repository.

Motivation and context

GitHub Container Registry is free for open source projects, whereas Docker Hub is only free for three or fewer users. (We are currently allowed four users because we are grandfathered in.)

Implementation notes

We already publish our Docker images to GHCR, so we would just need to:

• Change the workflows in this project to no longer publish to Docker Hub.
• Change Docker compositions and such in other repositories to pull from GHCR where necessary.