Migrate the webhook-certgen program to inside ingress repo (#7475)

images/kube-webhook-certgen/Makefile

@@ -0,0 +1,56 @@
+# Copyright 2021 The Kubernetes Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+.DEFAULT_GOAL:=build
+
+SHELL=/bin/bash -o pipefail -o errexit
+
+DIR:=$(strip $(shell dirname $(realpath $(lastword $(MAKEFILE_LIST)))))
+INIT_BUILDX=$(DIR)/../../hack/init-buildx.sh
+
+TAG ?=v$(shell date +%m%d%Y)-$(shell git rev-parse --short HEAD)
+REGISTRY ?= local
+
+IMAGE = $(REGISTRY)/kube-webhook-certgen
+
+# required to enable buildx
+export DOCKER_CLI_EXPERIMENTAL=enabled
+
+# build with buildx
+PLATFORMS?=linux/amd64,linux/arm,linux/arm64,linux/s390x
+OUTPUT=
+PROGRESS=plain
+
+build: ensure-buildx
+	docker buildx build \
+		--platform=${PLATFORMS} $(OUTPUT) \
+		--progress=$(PROGRESS) \
+		--pull \
+		-t $(IMAGE):$(TAG) rootfs
+
+# push the cross built image
+push: OUTPUT=--push
+push: build
+
+# enable buildx
+ensure-buildx:
+# this is required for cloudbuild
+ifeq ("$(wildcard $(INIT_BUILDX))","")
+	@curl -sSL https://raw.githubusercontent.com/kubernetes/ingress-nginx/main/hack/init-buildx.sh | bash
+else
+	@exec $(INIT_BUILDX)
+endif
+	@echo "done"
+
+.PHONY: build push ensure-buildx