Is SSL/HTTPS Needed Between Docker Containers on the Same Network?
Generally - no, I don't think you need TLS between your reverse proxy and service containers within same Docker network (or possibly 2 Docker networks: 1 internal for workers, 1 with internet access where reverse proxy sits and bridges the gap into internal network).
A wider answer would primarily depend on whether you trust your Docker host and services on it. Then consider how containers address each other, do they need to leave docker network (like public name resolution) at any time. And what you'd be looking for from TLS: identity verification or transport encryption. Each of those considerations would have some caveats.