Register RuntimeClass CRD as an addon

cluster/addons/runtimeclass/OWNERS

+approvers:
+- tallclair
+- dchen1107
+reviewers:
+- sig-node-reviewers

cluster/addons/runtimeclass/README.md

+# RuntimeClass
+
+RuntimeClass is an alpha feature for supporting multiple container runtimes within a cluster. When
+enabled, pods can select a RuntimeClass to run with using the `PodSpec.RuntimeClassName` field.
+
+To enable RuntimeClass, set the feature gate `RuntimeClass=true`, and ensure the CRD defined in this
+directory is installed.
+
+For more information, see:
+https://github.com/kubernetes/community/blob/master/keps/sig-node/0014-runtime-class.md
+
+[![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/cluster/addons/runtimeclass/README.md?pixel)]()

cluster/addons/runtimeclass/runtimeclass_crd.yaml

+kind: CustomResourceDefinition
+apiVersion: apiextensions.k8s.io/v1beta1
+metadata:
+  name: runtimeclasses.node.k8s.io
+  labels:
+    addonmanager.kubernetes.io/mode: Reconcile
+spec:
+  group: node.k8s.io
+  version: v1alpha1
+  versions:
+    - name: v1alpha1
+      served: true
+      storage: true
+  names:
+    plural:   runtimeclasses
+    singular: runtimeclass
+    kind:     RuntimeClass
+  scope: Cluster
+  validation:
+    openAPIV3Schema:
+      properties:
+        spec:
+          properties:
+            runtimeHandler:
+              type: string
+              pattern: '^[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*$'

cluster/gce/gci/configure-helper.sh

@@ -2498,11 +2498,15 @@ EOF
       setup-addon-manifests "addons" "istio/noauth"
     fi
   fi
+  if [[ "${FEATURE_GATES:-}" =~ "RuntimeClass=true" ]]; then
+    setup-addon-manifests "addons" "runtimeclass"
+  fi
   if [[ -n "${EXTRA_ADDONS_URL:-}" ]]; then
     download-extra-addons
     setup-addon-manifests "addons" "gce-extras"
   fi
 
+
   # Place addon manager pod manifest.
   cp "${src_dir}/kube-addon-manager.yaml" /etc/kubernetes/manifests
 }