Metrics need the namespace as label

[adejanovski]

We currently don't label the metrics scraped through Vector with the namespace in which the cluster is deployed.
This doesn't allow distinguishing two clusters in different namespaces that would have the same cluster and dc names from each other.
We need to add the namespace as env variable in the server system logger container, and use it to label the metrics (like we do for cluster, dc and rack names).