Fix CI Refactor

[bennibbelink]

Any images are now pushed to the ghcr of github.repository_owner instead of cyclus to prevent 403 forbidden errors when PRs originate from forks.

Also modifies the PR comment implementation to use a separate workflow - also to prevent permissions errors when PRs originate from forks.

[bennibbelink]

Example PR in my repo

[bennibbelink]

I think I have this working now. It is less clean than before but this is what happens for downstream testing:

1. build cycamore image and tag as ghcr.io/${{ github.repository_owner }}/cycamore_${{ matrix.ubuntu_versions }}_${{ matrix.pkg_mgr }}/cycamore:ci-image-cache
2. build cymetric using a build-context that maps ghcr.io/cyclus/cycamore_${{ matrix.ubuntu_versions }}_${{ matrix.pkg_mgr }}/cycamore:ci-image-cache to ghcr.io/${{ github.repository_owner }}/cycamore_${{ matrix.ubuntu_versions }}_${{ matrix.pkg_mgr }}/cycamore:ci-image-cache. This way even though we push the CI image to the collaborators registry we can still use it to build cymetric. I tried doing this locally using different output types in the docker/build-push-action but to no avail.

The test PR in my repo is almost working correctly except I'm running into the same issue we saw before where cycamore doesn't have permission to write cymetric packages. @gonuke where were you able to modify the package permissions? So far the only way I've found is to go to each package individually and Manage Actions access (still doesnt seem to have to an effect)
EDIT: working now, I had only given cycamore read permission for cymetric

[gonuke]

LGTM