[bug/feat]: REST and gRPC might be running on a different host than cln-application

While cln-application allows individually setting the PORT and PROTOCOL for REST and gRPC, it seems to assume they are running on the same host as cln-application (LIGHTNING_IP).

It would be desirable for cln-application to expose ENV variables for LIGHTNING_REST_HOST and LIGHTNING_GRPC_HOST in the case they are not the same as LIGHTNING_IP.