feat: allow specifying runtime class in runner spec (#580)

This allows using the `runtimeClassName` directive in the runner's spec.

One of the use-cases for this is Kata Containers, which use `runtimeClassName` in a pod spec as an indicator that the pod should run inside a Kata container. This allows us a greater degree of pod isolation.

controllers/runner_controller.go

@@ -910,6 +910,10 @@ func (r *RunnerReconciler) newPod(runner v1alpha1.Runner) (corev1.Pod, error) {
 		pod.Spec.HostAliases = runner.Spec.HostAliases
 	}
 
+	if runner.Spec.RuntimeClassName != nil {
+		pod.Spec.RuntimeClassName = runner.Spec.RuntimeClassName
+	}
+
 	if err := ctrl.SetControllerReference(&runner, &pod, r.Scheme); err != nil {
 		return pod, err
 	}