Pin tool versions with hack/go.mod (#5622)

* Pin tool versions with hack/go.mod

This change centralizes the tracking of versions for tools used for
development and testing. This way, the tools and all their
dependencies have their checksums stored in hack/go.sum, which
improves supply chain security.

* Workspace Sync & Tidy

hack/Makefile

@@ -0,0 +1,20 @@
+# Copyright 2019 The Kubernetes Authors.
+# SPDX-License-Identifier: Apache-2.0
+
+export KUSTOMIZE_ROOT ?= $(shell pwd | sed -E 's|(.*\/kustomize)/(.*)|\1|')
+include $(KUSTOMIZE_ROOT)/Makefile-modules.mk
+
+.PHONY: lint
+# No file to lint for this module
+lint:
+	true
+
+.PHONY: test
+# No tests for this module
+test:
+	true
+
+.PHONY: build
+# No command to build for this module
+build:
+	true