Ability to have no proxy listeners on egress workers with no inbound traffic

[chilicheech]

It would be great if we could omit the proxy listener for egress workers that have no inbound traffic, as when in private networks with a multi-hop setup. The egress worker establishes an outbound connection to the ingress worker. The client connects to the ingress worker, which sends traffic to the egress worker, which then reverse proxies the traffic to the targets. In this case there's no need for a proxy listener. But, when we omit the proxy listener boundary complains and fails to start.

This would help with not having to reserve ports for no practical reason when running multiple egress workers on a single baremetal host. Multiple egress workers may run on the same baremetal host for different reasons, one being if they connect to different upstream clusters.