Fix allow-prometheus NetworkPolicy

```bugfix operator
An issue causing a NetworkPolicy to do not allow egress from prometheus Pod to alertmanager and vpa-exporter Pods is now fixed.
```

Signed-off-by: ialidzhikov <i.alidjikov@gmail.com>

charts/seed-monitoring/charts/core/charts/prometheus/templates/allow-prometheus-network-policy.yaml

@@ -39,14 +39,13 @@ spec:
         matchLabels:
           component: alertmanager
           role: monitoring
-          garden.sapcloud.io/role: monitoring
       namespaceSelector:
         matchLabels:
           role: garden
     - podSelector:
         matchLabels:
           app: vpa-exporter
-          garden.sapcloud.io/role: vpa
+          gardener.cloud/role: vpa
       namespaceSelector:
         matchLabels:
           role: garden