Configuration file with the admissionConfig
vi /openshift.local.config/master/master-config.yaml
Pod Selector feature shows how configure https://docs.openshift.com/container-platform/3.9/admin_guide/scheduling/pod_placement.html#constraining-pod-placement-nodeselector
Example of webhook https://github.com/openshift/kubernetes-namespace-reservation
Webhook in minikube kubernetes/minikube#1264