Add PodMonitor to supported resources

Currently, `ServiceMonitor` is a supported resource type but `PodMonitor` is not. This means one can configure monitoring for Deployments, but not for things like DaemonSets. Our operator deploys a DaemonSet, which should ideally be scraped by Prometheus, hence we configure a PodMonitor. Could `PodMonitor` be added to the list of supported resources?