Description of problem:

Since RHIDP-11725, plugin references are being replaced to registry.access.redhat.com in the plugin catalog index image. But now, the mirroring script is failing to pull those references (because they are not released yet).

Steps to Reproduce

.rhdh/scripts/mirror-plugins.sh \
  --plugin-index oci://quay.io/rhdh/plugin-catalog-index:1.9 \
  --to-registry registry.localhost:5000

Actual results:

[INFO] Red Hat Developer Hub - Dynamic Plugin OCI Artifact Mirroring Script
[INFO] ======================================================================
[INFO] Starting plugin artifact mirroring...
[INFO] Resolving plugins from catalog index: oci://quay.io/rhdh/plugin-catalog-index:1.9
Getting image source signatures
Copying blob 546632789629 done   | 
Copying config 8d15d53569 done   | 
Writing manifest to image destination
[INFO] Found 51 unique plugins from catalog index
[INFO] Total unique plugins to mirror: 51
[INFO] Mirroring oci://registry.access.redhat.com/rhdh/backstage-community-plugin-acr@sha256:ea417c59bc28c5153b36e0ab877b0e88686f10f9c9d0f769367b12ebb5e5f4d3 to registry.localhost:5000/rhdh-plugins/rhdh/backstage-community-plugin-acr@sha256:ea417c59bc28c5153b36e0ab877b0e88686f10f9c9d0f769367b12ebb5e5f4d3...
FATA[0000] initializing source docker://registry.access.redhat.com/rhdh/backstage-community-plugin-acr@sha256:ea417c59bc28c5153b36e0ab877b0e88686f10f9c9d0f769367b12ebb5e5f4d3: reading manifest sha256:ea417c59bc28c5153b36e0ab877b0e88686f10f9c9d0f769367b12ebb5e5f4d3 in registry.access.redhat.com/rhdh/backstage-community-plugin-acr: unauthorized: access to the requested resource is not authorized

Expected results:

It should pass as this will make it easier to test mirroring a catalog index with plugins that we know are not released yet.
Similar to what was done in RHIDP-11773, it should fall back to pulling the image from quay.io/rhdh if the image does not exist on registry.access.redhat.com/rhdh

Reproducibility (Always/Intermittent/Only Once):

Always for unreleased plugins. But should not be an issue once plugins are published to registry.access.redhat.com (hence the priority set to Major).

Build Details:

Additional info (Such as Logs, Screenshots, etc):