Wire context for cert controllers

All the controllers should use context for signalling termination of communication with API server. Once kcm cancels context all the cert controllers which are started via kcm should cancel the APIServer request in flight instead of hanging around.

test/integration/certificates/controller_approval_test.go

@@ -98,10 +98,10 @@ func TestController_AutoApproval(t *testing.T) {
 			// Register the controller
 			c := approver.NewCSRApprovingController(client, informers.Certificates().V1().CertificateSigningRequests())
 			// Start the controller & informers
-			stopCh := make(chan struct{})
-			defer close(stopCh)
-			informers.Start(stopCh)
-			go c.Run(1, stopCh)
+			ctx, cancel := context.WithCancel(context.TODO())
+			defer cancel()
+			informers.Start(ctx.Done())
+			go c.Run(ctx, 1)
 
 			// Configure appropriate permissions
 			if test.grantNodeClient {