add webhook metrics to the "API Dashboard"

kube-apiserer records a number of metrcis for webhooks, this can be found here - https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/apiserver/pkg/admission/metrics/metrics.go

Add a subset of these metrics to the "API Performance" dashboard in OpenShift console

The source of the current API Performance dashboard is here - https://github.com/openshift/cluster-kube-apiserver-operator/blob/master/manifests/0000_90_kube-apiserver-operator_05_api_performance_dashboard.yaml

(It may make sense to add a new dashboard dedicated to webhook metrics, since there are quite a few metrics for webhook. currently the API performance dashboard already has many panels, but i would leave it to the engineer working on this to decide)