fix(data): set expiry on manifest list tags for existing manifests (PROJQUAY-7245)
When a manifest list was pushed with multiple tags, only the first tag
got the expiration from child manifest labels. Subsequent tags showed
"Never" because list_manifest_labels() only checked labels directly on
the manifest list, not on child manifests.
Added _get_expiry_label_for_manifest() helper that properly queries
child manifest labels for manifest lists, matching the intersection
logic used during initial manifest creation.
Co-authored-by: Brady Pratt <bpratt@redhat.com>
Co-authored-by: Claude <noreply@anthropic.com>