[PCFF-1975] Emit "false" and "0" for bools and ints where appropriate.

[henryguillen]

See grpc-ecosystem/grpc-gateway#233

This is coming to grpc-gateway-v2, but we need to accelerate this due to the fact that we need to be able to build a C# proxy that is JSON-compatible with the pb-go serializer used in the gateway.

This is a breaking change, but it is also more reasonable. See a similar change in a public fork of the gateway flw-cn/grpc-gateway@aa60176

1. i'm not actually sure even if we merge this whether we can build a compatible C# implementation using Newtonsoft.Json serialization.
2. we would probably want to make this an optional change for our gateways

But hell if I'm gonna build this myself.