dch-webhooks: Configure SSH cert signer

The *dch-webhooks* tool now provides an operation for hosts to request a
signed SSH certificate from the SSH CA.  It's primarily useful for
unattended deployments like CoreOS Ignition, where hosts do not have
any credentials to authenticate with the CA directly.

dch-root-ca/kustomization.yaml

@@ -0,0 +1,7 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+configMapGenerator:
+- name: dch-root-ca
+  files:
+  - dch-root-ca.crt