Exception recording in AspNetCore instrumentation

[cijothomas]

For AspNetCore instrumentation:
We have the ability to get exception from the diagnosticsource. We can add an ability to enrich the activity with this exception. Semantic conventions are here for exception: https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/semantic_conventions/exceptions.md

https://github.com/dotnet/aspnetcore/blob/3fdbc2e90d9762324ef3809098c9ca25b0cb3284/src/Middleware/Diagnostics/src/ExceptionHandler/ExceptionHandlerMiddleware.cs#L141

https://github.com/dotnet/aspnetcore/blob/3892b4ea82b64aa7abe0a87c4277449c26b47c9c/src/Hosting/Hosting/src/Internal/HostingApplicationDiagnostics.cs#L231