[Feature]: add metricRelabelings field to the dcgm exporter service monitor.

[xhejtman]

The operator already supports relabelings, but not the metricRelabelings. If I want to avoid exported_namespace and exporeted_pod labels and use the namespace and pod instead, I can do it with:

  metricRelabelings:
        - action: replace
          regex: (.+)
          sourceLabels:
            - exported_namespace
          targetLabel: namespace
        - action: replace
          regex: (.+)
          sourceLabels:
            - exported_pod
          targetLabel: pod
        - action: replace
          regex: (.+)
          sourceLabels:
            - exported_container
          targetLabel: container

but this is currently not possible from the helm values.

[kvnloo]

This looks like a fairly small extension of the existing relabelings path.

I would propose keeping the first PR limited to plumbing an optional metricRelabelings field through the existing DCGM Exporter ServiceMonitor configuration:

• values / API field;
• ServiceMonitor rendering;
• generated schema/docs if required by the existing workflow;
• tests for omitted, empty, and populated values;
• no change to the current relabelings behavior.

That would allow rules such as rewriting exported_namespace, exported_pod, and exported_container without introducing any exporter-side behavior.

Since this issue is currently lifecycle/frozen, I don't want to open implementation work without a maintainer signal. Would that narrow scope be useful?