Is your feature request related to a problem? Please describe.
We are using grafana-agent to scrape metrics, which uses a label selector to scrape only certain services. To allow monitoring our cluster, we have to set a custom label on the podMonitor.

Describe the solution you'd like
Add a global custom label feature to the podMonitors.

Describe alternatives you've considered
We could add the possibility on a per service basis, this could be added later.