[.NET] Add tools for Ollama

[DavidLuong98]

Why are these changes needed?

• We want to add tools for ollama
• Ollama API now supports tools, update AutoGen.OllamaChatClient to support this latest feature as well.

Related issue number

#3226

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.