feat: configure k8s recommended labels on subresources

[GabriFedi97]

Add Kubernetes recommended labels to Role and RoleBinding managed Objects:

app.kubernetes.io/name: "postgresql"
app.kubernetes.io/instance: "<cluster name>"
app.kubernetes.io/version: "<cluster pg major version>"
app.kubernetes.io/component: "database"
app.kubernetes.io/managed-by: "plugin-barman-cloud"

Notice that some label values are a bit different from what described in the issue.

closes #545