Make the controller-gen target non user-facing

Makefile

@@ -148,7 +148,7 @@ deploy: patch-image manifests
 	kustomize build config/overlays/dev | kubectl apply -f -
 
 # Generate manifests e.g. CRD, RBAC etc.
-manifests: controller-gen
+manifests: __controller-gen
 	$(CONTROLLER_GEN) $(CRD_OPTIONS) rbac:roleName=manager-role webhook paths="./apis/..." paths="./pkg/..." output:crd:artifacts:config=config/crd/bases
 	rm -rf manifest_staging
 	mkdir -p manifest_staging/deploy
@@ -160,7 +160,7 @@ lint:
 	golangci-lint -v run ./... --timeout 5m
 
 # Generate code
-generate: controller-gen target-template-source
+generate: __controller-gen target-template-source
 	$(CONTROLLER_GEN) object:headerFile=./hack/boilerplate.go.txt paths="./apis/..." paths="./pkg/..."
 
 # Docker Login
@@ -256,9 +256,7 @@ promote-staging-manifest:
 uninstall:
 	kustomize build config/overlays/dev | kubectl delete -f -
 
-# find or download controller-gen
-# download controller-gen if necessary
-controller-gen: __tooling-image
+__controller-gen: __tooling-image
 CONTROLLER_GEN=docker run -v $(shell pwd):/gatekeeper gatekeeper-tooling controller-gen
 
 __tooling-image: