Add gRPC Server Reflection support

Is your feature request related to a problem? Please describe.
gRPC and connect-go support a server-side reflection API that serves protobuf schema information to clients. As of now, connect-node does not support this feature.

This feature would be useful as various gRPC debugging utilities can use it to grab schema information on-demand.

Describe the solution you'd like
Ideally, connect-node would have an optional implementation of serverside reflection, including the necessary code generation in protobuf-es to support this (as needed.)

Additional context
gRPC Server Reflection Protocol
connect-go grpcreflect implementation