docs: document template.metadata labels/annotations behavior (#6102)

docs/snippets/full-external-secret.yaml

@@ -56,6 +56,10 @@ spec:
       type: kubernetes.io/dockerconfigjson # or TLS...
 
       metadata:
+        # Labels and annotations to set on the Secret.
+        # When a template is defined, these replace the default behavior
+        # of copying labels and annotations from the ExternalSecret.
+        # Set to an empty map ({}) to prevent any labels or annotations from being copied.
         annotations: {}
         labels: {}
         # The finalizers will be added to the Secret.