chore: fix CI workflow

[janishorsts]

Fixes EarthBuild 1st release (view)

Attempt to run the CI workflow successfully by keeping the changes to a minimum and retaining existing outcomes.

I did my best to avoid unnecessary changes, but got carried away a little bit with exploratory research about how it works:

• Import Earthfiles from @EarthBuild repositories.
• Configure ubuntu-latest to complete +test successfully.
• Added mirror.gcr.io and public.ecr.awr mirrors
• Test images are pushed to the private GitHub Container Registry https://github.com/EarthBuild/dind/pkgs/container/dindtest. Initially, I pushed the test images to the Docker registry, but I switched over to the GitHub Container Registry (GHCR). I have no experience working with GHCR, but I hope it offers a better and more stable experience.
• Renamed DOCKERHUB_USER to CR_ORG to avoid confusion and reflect intent clearly (CR - Container Registry).
• Added CR_HOST to allow pushing images to any container registry.
• Ubuntu 23.04 has reached EOL. To avoid any friction for users migrating to @EarthBuild, I retained this dind image.
• I manually tested the generated Alpine dind in a few projects and it runs fine

[gilescope]

GHCR is good. No complaints.

[gilescope]

LGTM