.Net: [Feature]: Content Understanding support for agent framework

### Description

Support for content understanding like with the sdk for python

### Code Sample

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### Language/SDK

.NET

Start by locating the existing Python SDK implementation for content understanding and the corresponding .NET agent-framework entry point. Compare their public behavior and identify the relevant .NET tests; done means the .NET SDK provides equivalent content-understanding support with test coverage.

Written by the indexing model from the issue text.