.NET: Structured output improvements

[SergeyMenshykh]

This issue tracks structured output improvements for V1.

Related issues:

• .NET: Structured Output calling does not work with lists/array if ResponseFormat is used, but works if .RunAsync<> is used #2874
• .NET - No Built-in Support for AgentRunResponse Deserialization to Structured Types #2683
• .NET: Cannot invoke RunAsync<T> on agent that uses telemetry #1642
• .NET feedback: Structured output feels more cumbersome in AF + Have issues with Enums in result object #1057