v9.3.1 -- fix installer-anaconda-iso/qcow2-bake digest-pinning bug

Both components could not actually carry a digest-qualified `image`
input (repo@sha256:...): the docker pull + docker-daemon skopeo bridge
failed closed on every digest-qualified reference (Docker Engine's
classic local image store does not preserve original registry manifest
bytes). Fixed by fetching directly via skopeo's docker:// transport into
containers-storage, bypassing docker pull and the docker-daemon bridge
entirely. Also corrects both components' header comments (and the
catalog README) about triggering a standalone config file: a
CI_CONFIG_PATH pipeline variable does not work, per confirmed GitLab
limitations gitlab-org/gitlab-foss#60331 and gitlab-org/gitlab#27987.

Patch bump: no existing consumer passes a digest-qualified image today,
so nothing working changes behavior.