.NET: Add Function Tool Use Cases

[azarboon]

Motivation and Context

Function tools are ideal for scenarios where determinism and predictability are critical, helping users avoid potential issues. This aspect is not currently documented on GitHub or Microsoft Learn. Since this example demonstrates a Function Tool, this update addresses that gap by highlighting potential use cases and benefits of this approach. The current example is simple and may cause users to underestimate the advantages of using Function Tools.

Description

This update is purely documentation and introduces no code changes. It adds content clarifying the use cases and potential benefits of Function Tools to guide users effectively.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• [] Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR. No it's not a breaking change