AI Integration: Get Request size from request diagnostics and optimize logic to get Response Size

[sourabh1007]

1. Expose an API in CosmosTraceDiagnostics to get request size out of diagnostics and use it in open telemetry.
2. Right now, We are getting response size from stream or header content length. We should find a way to get response size in all the cases irrespective of availability of it in stream and header. ref [PREVIEW] AI Integration: Adds open telemetry support for most of the Operations #3277 (comment)