relates to GRU-69
Modifies replicasync to handle discovering NATS enabled primary replicas explicitly, and passing that info to the NATS Pubsub.
This PR adds a new deployment value to explicitly represent the host or IP that the replica can be reached on. It isn't wired up to the CLI, but piggybacks on the DERP config for now.
We learn the NATS port directly from NATS at runtime, and propagate it thru replicasync to learn all peers for clustering.
Spike Curtis