I want to enable Kubernetes Engine Monitoring on clusters but I don't see that as a field in Terraform's google_container_cluster resource.
Is Kubernetes Engine Monitoring managed with another resource?
You can use the newer Kubernetes Monitoring Service by setting monitoring_service to monitoring.googleapis.com/kubernetes instead of the default monitoring.googleapis.com.
When enabling this you will also need to set logging_service to logging.googleapis.com/kubernetes as well.