move the extra labels to a metrics

[amnonh]

Currently, cluster and DC labels are added to metrics in the Prometheus configuration. In addition, some users enrich their metrics by adding even more labels.

There are a few downsides to this approach:

• Memory usage: each of those labels is stored again and again per metrics
• It's harder to configure and update those labels.

The alternative is to put all the extra labels on a metric and use join to add the labels to the existing labels when needed