[#246] Optimize backend base image build process

This commit optimizes the build process for the backend base Docker
image in the `scripts/govtool/Makefile`. It introduces conditional logic
to build or push the base image only if it doesn't already exist in the
repository, significantly reducing unnecessary builds and pushes,
thereby saving time and resources.

Key changes include:
- The `build-backend` target now depends on `build-backend-base`,
  ensuring the base image is available before building the backend
  image. However, the base image will only be built if it is not already
  present, as checked by `docker manifest inspect`.
- Similarly, `push-backend-base` incorporates a condition to push the
  base image only if it is not already available in the repository,
  using `docker manifest inspect` to verify its existence.

This logic prevents redundant builds and uploads of the base image when
no changes have occurred to the `vva-be.cabal` file, making the CI/CD
pipeline more efficient. By building the base image only when necessary,
we align with best practices for Docker image management and optimize
our deployment workflow.

scripts/govtool/Makefile

@@ -65,7 +65,7 @@ upload-config: prepare-config
 	rsync -av -e 'ssh -o StrictHostKeyChecking=no' config/target/. $(ssh_url):config
 
 .PHONY: build-backend
-build-backend:
+build-backend: build-backend-base
 	@:$(call check_defined, cardano_network)
 	@:$(call check_defined, env)
 	$(docker) build --build-arg BASE_IMAGE_TAG=$(base_backend_image_tag) --tag "$(repo_url)/backend:$(tag)" ../../govtool/backend
@@ -74,11 +74,12 @@ build-backend:
 build-backend-base:
 	@:$(call check_defined, cardano_network)
 	@:$(call check_defined, env)
+	docker manifest inspect "$(repo_url)/backend-base:$(base_backend_image_tag)" || \
 	$(docker) build --file ../../govtool/backend/Dockerfile.base --tag "$(repo_url)/backend-base:$(base_backend_image_tag)" ../../govtool/backend
-	@echo "New backend-base image: $(repo_url)/backend-base:$(base_backend_image_tag)"
+	@echo "Using backend-base image: $(repo_url)/backend-base:$(base_backend_image_tag)"
 
 .PHONY: push-backend
-push-backend: docker-login
+push-backend: docker-login push-backend-base
 	@:$(call check_defined, cardano_network)
 	@:$(call check_defined, env)
 	$(docker) push $(repo_url)/backend:$(tag)
@@ -87,6 +88,7 @@ push-backend: docker-login
 push-backend-base: docker-login
 	@:$(call check_defined, cardano_network)
 	@:$(call check_defined, env)
+	docker manifest inspect "$(repo_url)/backend-base:$(base_backend_image_tag)" || \
 	$(docker) push $(repo_url)/backend-base:$(base_backend_image_tag)
 
 .PHONY: build-frontend