Option to set namespace for ServiceMonitor

[JElgar]

Description
Currently when enabling monitoring the ServiceMonitor is installed in the same namespace as the other resources. It would be nice if a namespace could be specified in values for the ServiceMonitor (so that it can be put in the same namespace as other monitoring resources)

Basic example

Example values

serviceMonitor:
  enabled: true
  namespace: observability

Other

This might be a bad idea as it seems you can update Prometheus to detect ServiceMonitors in other namespaces. Its not very clear to me but it seems that having all monitoring resources in one namespace is also a valid pattern so if thats the case then I think this is a good option to have. Either way happy to help out with this if you think its worth doing.