To fix multi-arch build, replace docker-buildx target in project Makefile

In the project Makefile, replace existing docker-buildx target with following definition.

docker-buildx: ## Build and push docker image for the manager for cross-platform support
	- docker buildx create --name project-v3-builder
	docker buildx use project-v3-builder
	- docker buildx build --push --platform=$(PLATFORMS) --tag ${IMG} -f Dockerfile .
	- docker buildx rm project-v3-builder

See #6661 for more details.

Last modified February 29, 2024: Release v1.34.0 (#6688) (4abd483a)