Decouple `upload-service` from `back-end`

Right now the back-end runs the upload service in the same docker image as the php; this means there is a weird coupling between back-end's `Dockerfile.dev` that doesn't quite belong.  For instance: if we update node in upload service we need to update the `back-end` repository as well.

I believe it would be better to have the services separated / upload service running in its own container.