Description of problem:
Instead of using the application/vnd.docker.distribution.manifest.list.v2+json format the application/vnd.oci.image.index.v1+json format is used.
This is causing issues when mirroring these images to older registries which do not support the newer manifest formats.

Actual results:
Images use the new manifest format.
 application/vnd.oci.image.index.v1+json

examples)
$ skopeo inspect --raw docker://registry.redhat.io/cluster-observability-operator/cluster-observability-rhel9-operator:1.2.2-1752661671 | jq -rM .mediaType
application/vnd.oci.image.index.v1+json

$ skopeo inspect --raw docker://registry.redhat.io/cluster-observability-operator/dashboards-console-plugin-0-4-rhel9:1.2.2-1752687226 | jq -rM .mediaType
application/vnd.oci.image.index.v1+json

$ skopeo inspect --raw docker://registry.redhat.io/cluster-observability-operator/distributed-tracing-console-plugin-1-0-rhel9:1.2.2-1752687310 | jq -rM .mediaType
application/vnd.oci.image.index.v1+json

$ skopeo inspect --raw docker://registry.redhat.io/cluster-observability-operator/korrel8r-rhel9:1.2.2-1752659953 | jq -rM .mediaType
application/vnd.oci.image.index.v1+json

$ skopeo inspect --raw docker://registry.redhat.io/cluster-observability-operator/logging-console-plugin-6-1-rhel9:1.2.2-1752686634 | jq -rM .mediaType
application/vnd.oci.image.index.v1+json

Expected results:
Images continue to use the older manifest format.
 application/vnd.docker.distribution.manifest.list.v2+json