add makefile to support image building, pushing & tagging

https://github.com/fphammerle/docker-onion-service/blob/e8dfe51bb831c54d9a87be7c70f3f79e2f45d9ce/Makefile

Makefile

@@ -0,0 +1,34 @@
+# sync with https://github.com/fphammerle/docker-onion-service/blob/master/Makefile
+
+IMAGE_NAME = docker.io/fphammerle/postfix
+PROJECT_VERSION = $(shell git describe --match=v* --abbrev=0 --dirty | sed -e 's/^v//')
+POSTFIX_PACKAGE_VERSION = $(shell grep -Po 'POSTFIX_PACKAGE_VERSION=\K.+' Dockerfile | tr -d -)
+ARCH = $(shell arch)
+# architecture[arm_variant]
+# https://github.com/opencontainers/image-spec/blob/v1.0.1/image-index.md#image-index-property-descriptions
+IMAGE_TAG_ARCH_aarch64 = arm64
+IMAGE_TAG_ARCH_armv6l = armv6
+IMAGE_TAG_ARCH_armv7l = armv7
+IMAGE_TAG_ARCH_x86_64 = amd64
+IMAGE_TAG_ARCH = ${IMAGE_TAG_ARCH_${ARCH}}
+IMAGE_TAG = ${PROJECT_VERSION}-postfix${POSTFIX_PACKAGE_VERSION}-${IMAGE_TAG_ARCH}
+BUILD_PARAMS = --tag="${IMAGE_NAME}:${IMAGE_TAG}" \
+	--build-arg=REVISION="$(shell git rev-parse HEAD)"
+
+.PHONY: worktree-clean docker-build podman-build docker-push
+
+worktree-clean:
+	git diff --exit-code
+	git diff --staged --exit-code
+
+docker-build: worktree-clean
+	sudo docker build ${BUILD_PARAMS} .
+
+podman-build: worktree-clean
+	# --format=oci (default) not fully supported by hub.docker.com
+	# https://github.com/docker/hub-feedback/issues/1871#issuecomment-748924149
+	podman build --format=docker ${BUILD_PARAMS} .
+
+docker-push: docker-build
+	sudo docker push "${IMAGE_NAME}:${IMAGE_TAG}"
+	@echo git tag --sign --message '$(shell sudo docker image inspect --format '{{join .RepoDigests "\n"}}' "${IMAGE_NAME}:${IMAGE_TAG}")' docker/${IMAGE_TAG} $(shell git rev-parse HEAD)