Example of how to integrate a client for another gRPC service

## Feature Request

### Motivation

I appreciate the effort that has been put into the examples and documentation for this project. However, I could not easily find an example of what to do when calling another gRPC service from inside a server.

Specifically, I have the protobuf service definitions for another service, and I need to generate a client from them and call it. There are namespace conflicts between it and the protobuf definition of my own service.

Right now, to work around this, I have created a subcrate that builds the client protobuf. Is there a better way to do this? The meaning of some of the functions in `build.rs` is often opaque, and it is very likely that I have missed something. Thank you.

Start with the existing examples and the project's build.rs guidance for generating protobuf clients. Determine how an application can generate and call a client for another gRPC service without namespace conflicts, including whether the subcrate workaround is necessary. Done means adding a clear, runnable example or documentation that demonstrates the supported integration pattern.

Written by the indexing model from the issue text.