feat: RunnerDeployment

Adds the initial version of RunnerDeployment that is intended to manage RunnerSets(#1), like Deployment manages ReplicaSets.

This is the initial version and therefore is bare bone. The only update strategy it supports is `Recreate`, which recreates the underlying RunnerSet when the runner template changes. I'd like to add `RollingUpdate` strategy once this is merged.

This depends on #1 so the diff contains that of #1, too. Please see only the latest commit for review.

Also see https://github.com/mumoshu/actions-runner-controller-ci/runs/471329823?check_suite_focus=true to confirm that `make tests` is passing after changes made in this commit.

controllers/runnerset_controller_test.go

@@ -98,11 +98,13 @@ var _ = Context("Inside of a new namespace", func() {
 					},
 					Spec: actionsv1alpha1.RunnerSetSpec{
 						Replicas: intPtr(1),
-						Template: actionsv1alpha1.RunnerSpec{
-							Repository: "foo/bar",
-							Image:      "bar",
-							Env: []corev1.EnvVar{
-								{Name: "FOO", Value: "FOOVALUE"},
+						Template: actionsv1alpha1.RunnerTemplate{
+							Spec: actionsv1alpha1.RunnerSpec{
+								Repository: "foo/bar",
+								Image:      "bar",
+								Env: []corev1.EnvVar{
+									{Name: "FOO", Value: "FOOVALUE"},
+								},
 							},
 						},
 					},