Initial multi-arch image commit (#86)

Adding multi-arch image support for `arm64` and `amd64`. This uses dockers new `buildx` feature, to enable further architectures more work will be required to update the `runner/Dockerfile` file to pull architecture-specific releases.

The Makefile targets really should only be used for local testing and not for release, additional work to appropriately tag the release images may need to be added but for now, I've not added that logic.

Fixes: #86 

Signed-off-by: Michael Fornaro <20387402+xUnholy@users.noreply.github.com>

Makefile

@@ -11,6 +11,23 @@ else
 GOBIN=$(shell go env GOBIN)
 endif
 
+# default list of platforms for which multiarch image is built
+ifeq (${PLATFORMS}, )
+	export PLATFORMS="linux/amd64,linux/arm64"
+endif
+
+# if IMG_RESULT is unspecified, by default the image will be pushed to registry
+ifeq (${IMG_RESULT}, load)
+	export PUSH_ARG="--load"
+    # if load is specified, image will be built only for the build machine architecture.
+    export PLATFORMS="local"
+else ifeq (${IMG_RESULT}, cache)
+	# if cache is specified, image will only be available in the build cache, it won't be pushed or loaded
+	# therefore no PUSH_ARG will be specified
+else
+	export PUSH_ARG="--push"
+endif
+
 all: manager
 
 # Run tests
@@ -62,6 +79,18 @@ docker-build: test
 docker-push:
 	docker push ${NAME}:${VERSION}
 
+docker-buildx:
+	export DOCKER_CLI_EXPERIMENTAL=enabled
+	@if ! docker buildx ls | grep -q container-builder; then\
+		docker buildx create --platform ${PLATFORMS} --name container-builder --use;\
+	fi
+	docker buildx build --platform ${PLATFORMS} \
+		--build-arg RUNNER_VERSION=${RUNNER_VERSION} \
+		--build-arg DOCKER_VERSION=${DOCKER_VERSION} \
+		-t "${NAME}:${VERSION}" \
+		-f Dockerfile \
+		. ${PUSH_ARG}
+
 # Generate the release manifest file
 release: manifests
 	cd config/manager && kustomize edit set image controller=${NAME}:${VERSION}