Fix Docker multi-arch build by using buildx directly (#1935)

* Initial plan

* Fix Docker push by using buildx for multi-arch builds

Replace separate docker build commands with docker buildx build that
properly handles multi-platform builds. This fixes the "is a manifest
list" error that occurred when trying to create manifests from images
built with docker build --platform.

The new approach uses docker buildx build with --platform
linux/amd64,linux/arm64 to build both architectures in one command
and pushes them directly with the --push flag.

Co-authored-by: jordanstephens <706922+jordanstephens@users.noreply.github.com>

* Remove unused Docker image variables

Co-authored-by: jordanstephens <706922+jordanstephens@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jordanstephens <706922+jordanstephens@users.noreply.github.com>

Author: Copilot

src/Makefile

@@ -191,51 +191,18 @@ PROJECT_NAME := defang-cli
 DOCKER_REPO:=defangio
 DOCKER_IMAGE_NAME:=$(DOCKER_REPO)/$(PROJECT_NAME)
 
-DOCKER_IMAGE_ARM64:=$(DOCKER_IMAGE_NAME):arm64-$(VERSION)
-DOCKER_IMAGE_AMD64:=$(DOCKER_IMAGE_NAME):amd64-$(VERSION)
-
-.PHONY: image-amd64
-image-amd64:
-	docker build \
-	  --platform linux/amd64 \
-	  -t ${PROJECT_NAME} \
-	  -t $(DOCKER_IMAGE_AMD64) \
-	  --build-arg VERSION=$(VERSION) \
-	  --build-arg GO_VERSION=$(GO_VERSION) \
-	  .
-
-.PHONY: image-arm64
-image-arm64:
-	docker build \
-	  --platform linux/arm64 \
-	  -t ${PROJECT_NAME} \
-	  -t $(DOCKER_IMAGE_ARM64) \
+## Build and push multi-arch Docker images
+.PHONY: push-images
+push-images: login
+	docker buildx build \
+	  --platform linux/amd64,linux/arm64 \
+	  --push \
+	  -t $(DOCKER_IMAGE_NAME):$(VERSION) \
+	  -t $(DOCKER_IMAGE_NAME):latest \
 	  --build-arg VERSION=$(VERSION) \
 	  --build-arg GO_VERSION=$(GO_VERSION) \
 	  .
 
-## Build all docker images and manifest
-.PHONY: images
-images: image-amd64 image-arm64
-
-## Push all docker images
-.PHONY: push-images
-push-images: images login
-	docker push $(DOCKER_IMAGE_AMD64)
-	docker push $(DOCKER_IMAGE_ARM64)
-	docker manifest create --amend \
-	  $(DOCKER_IMAGE_NAME):$(VERSION) \
-	  $(DOCKER_IMAGE_AMD64) \
-	  $(DOCKER_IMAGE_ARM64)
-	docker manifest create --amend \
-	  $(DOCKER_IMAGE_NAME):latest \
-	  $(DOCKER_IMAGE_AMD64) \
-	  $(DOCKER_IMAGE_ARM64)
-	docker manifest push --purge \
-	  $(DOCKER_IMAGE_NAME):$(VERSION)
-	docker manifest push --purge \
-	  $(DOCKER_IMAGE_NAME):latest
-
 ## Login to docker
 .PHONY: login
 login: