Add gRPC streaming for code first approach

There is no approach using gRPC streaming in .Net Code First approach.
One of the solution is to use IAsyncEnumerable but it is not for a streaming but mostly about duplex connection.

P.S. If using protobuff first approach it works fine but in .Net ecosystem I would like rather use code first approach with Code First Grpc Reflection to provide contracts to other services that sending protofiles.

The issue names the .NET Code First approach, IAsyncEnumerable, and Code First Grpc Reflection, but no files or tests. Start by comparing the existing proto-first streaming behavior with the Code First path. Done means gRPC streaming contracts work through the Code First approach and can be exposed through reflection.

Written by the indexing model from the issue text.