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.

main.go

@@ -121,6 +121,17 @@ func main() {
 		setupLog.Error(err, "unable to create controller", "controller", "RunnerSet")
 		os.Exit(1)
 	}
+
+	runnerDeploymentReconciler := &controllers.RunnerDeploymentReconciler{
+		Client: mgr.GetClient(),
+		Log:    ctrl.Log.WithName("controllers").WithName("RunnerDeployment"),
+		Scheme: mgr.GetScheme(),
+	}
+
+	if err = runnerDeploymentReconciler.SetupWithManager(mgr); err != nil {
+		setupLog.Error(err, "unable to create controller", "controller", "RunnerDeployment")
+		os.Exit(1)
+	}
 	// +kubebuilder:scaffold:builder
 
 	setupLog.Info("starting manager")