Currently servers exchange information about their WAN serf port
and RPC port with serf tags, so that they all learn of each other's
addressing information. We intend to make larger use of the new
public-facing gRPC port exposed on all of the servers, so this PR
addresses that by passing around the gRPC port via serf tags and
then ensuring the generated consul service in the catalog has
metadata about that new port as well for ease of non-serf-based lookup.
R.B. Boyer