Support Configurable Allowlist Of Namespaces For Platform Monitoring

On OpenShift Dedicated, we have a desire to only monitor specific namespaces that we deem "platform" OSD-related components. We want only these namespaces to be monitored and alerted upon. Similar to scenario 2 in MON-1633, but with an explicit list of namespaces to only scrape with the `openshift.io/cluster-monitoring: "true"` label.

Done Criteria

• The ability for the platform monitoring stack to accept a list of namespaces via ConfigMap or other means that restricts namespace scraping to only that list of namespaces.