Add an announcement_address field to node config

[eauxxs]

In some cases, the service is deployed behind NATS, and the listening address of the service is 0.0.0.0:9735. Then node_announcement is 0.0.0.0, so is it possible to add a field so that the service deployed behind NATS can cooperate with port forwarding?

[rleed]

I need this too.

[npslaney]

+1 on this one