kubeRestartDeployment: Add function

The `kubeRestartDeployment` function restarts a Kubernetes deployment
using `kubectl rollout restart`.  This command is run in a dedicated
pod, with the `kubectl` binary bind-mounted from the host.

vars/kubeRestartDeployment.groovy

@@ -0,0 +1,34 @@
+@groovy.transform.Field
+def POD_YAML = '''\
+spec:
+  containers:
+  - name: jnlp
+    volumeMounts:
+    - name: kubectl
+      mountPath: /bin/kubectl
+      readOnly: true
+  volumes:
+  - name: kubectl
+    hostPath:
+      path: /usr/bin/kubectl
+      type: File
+'''
+
+def call(args) {
+    def namespace = args?.namespace
+    def name = args?.name
+
+    if (name == null) {
+        name = env.JOB_NAME.split('/')[1]
+    }
+
+    if (namespace == null) {
+        namespace = name
+    }
+
+    podTemplate(yaml: POD_YAML) {
+        node(POD_LABEL) {
+            sh "kubectl rollout restart deployment -n ${namespace} ${name}"
+        }
+    }
+}