dev(Makefile): Force linux/amd64 runtime selection

We want to support using Apple Silicon systems to develop Toolhub.
Providing native arm64 container images in addition to amd64 images
would be the most ideal solution, but a (hopefully) lower effort
solution is to instruct Docker to prefer a amd64 runtime and correct any
fallout from incompatibilities those images may have when running under
a QEMU emulator.

Change-Id: I94638a1fe97cbead88a184d45a3b951d98d69c3a

Makefile

@@ -38,7 +38,7 @@ help:
 .PHONY: help
 
 start: .env  ## Start the docker-compose stack
-	$(COMPOSE) up --build --detach
+	DOCKER_DEFAULT_PLATFORM=linux/amd64 $(COMPOSE) up --build --detach
 .PHONY: start
 
 stop:  ## Stop the docker-compose stack