[DISCUSS] Change Flight ListFlights return value to stream of FlightDescriptor

[Jacques Nadeau]

Right now, the ListFlights method returns a stream of FlightGetInfo (to be
renamed FlightInfo). This actually turns out to be quite expensive in many
cases since splits have to be generated. I'd like to propose changing this
method to return a stream of FlightDescriptors instead. What do people
think?

rpc ListFlights(Criteria) returns (stream FlightGetInfo) {}

to

rpc ListFlights(Criteria) returns (stream FlightDescriptor) {}