Provide backup-operator specific label

Signed-off-by: Víctor Cuadrado Juan <[email protected]>

Author: viccuad

docs/howtos/policy-servers/02-private-registry.md

@@ -49,13 +49,22 @@ kubectl --namespace kubewarden create secret docker-registry secret-ghcr-docker
 
 :::tip
 Label the secret as follows for it to be part of the backups of
-Rancher Backup Operator:
+Rancher Backup Operator.
+
+Either:
 
 ```shell
 $ kubectl label secret secret-ghcr-docker \
     app.kubernetes.io/part-of=kubewarden
 ```
 
+Or:
+
+```shell
+$ kubectl label secret secret-ghcr-docker \
+    resources.cattle.io/backup=true
+```
+
 ::::
 
 For more information on how to create the Docker Secrets, see the [Kubernetes documentation](https://kubernetes.io/docs/concepts/configuration/secret/#docker-config-secrets).