Use platform flag for image building (#13)

Use --platform instead of --arch

Makefile

@@ -91,7 +91,7 @@ run: manifests generate fmt vet ## Run a controller from your host.
 # More info: https://docs.docker.com/develop/develop-images/build_enhancements/
 .PHONY: docker-build
 docker-build: ## Build docker image with the manager.
-	$(CONTAINER_TOOL) build -t ${IMG} --arch linux/amd64 .
+	$(CONTAINER_TOOL) build -t ${IMG} --platform linux/amd64 .
 
 .PHONY: docker-push
 docker-push: ## Push docker image with the manager.