Add information about gRPC binary logging

At [gRPConf 2025](https://events.linuxfoundation.org/grpconf/program/schedule/) today, @AgraVator and @yashykt gave an excellent talk about gRPC observability. One section of the talk mentioned gRPC binary logging:


However, when I asked them after the talk about docs for binary logging, we were all surprised that we couldn't find much. Please add docs for binary logging. Some suggested topics (mostly from the slides above):

- which language implementations support it
- how to enable it with GRPC_BINARY_LOG_CONFIG
- security settings
- how to use binary logging
- troubleshooting services, finding exceptions
- load testing
- replaying RPCs from production
- translate to text for manual inspection or diffing with previous RPCs

I and a few coworkers attending this talk were delighted to see this slide and we're looking forward to learning how to use it!