OpenTelemetry OnException events

### What version of gRPC and what language are you using?
Grpc `2.39.0`

### What operating system (Linux, Windows,...) and version?
`Linux`

### What runtime / compiler are you using (e.g. .NET Core SDK version `dotnet --info`)
`.net5`

### What did you do?
I'm trying to use OpenTelemetry instrumentation in grpc server. It works fine except errors - they never get captured by OpenTelemetry. Based on https://github.com/open-telemetry/opentelemetry-dotnet-contrib/issues/1743 "Exception" events are not being emitted by the grpc library. Is there a plan to support `OnException` events going forward?

### What did you expect to see?
OpenTelemetry captures errors from grpc endpoints

### What did you see instead?

Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).

See [TROUBLESHOOTING.md](https://github.com/grpc/grpc-dotnet/blob/master/TROUBLESHOOTING.md) for how to diagnose problems better.

### Anything else we should know about your project / environment?

No file or test is named. Start by reading the gRPC server OpenTelemetry instrumentation and the linked opentelemetry-dotnet-contrib issue to understand the missing OnException events; define the expected exception event behavior and add coverage showing that endpoint errors are captured.

Written by the indexing model from the issue text.