[.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.

[rysweet]

This PR is against AutoGen 0.2. AutoGen 0.2 has been moved to the 0.2 branch. Please rebase your PR on the 0.2 branch or update it to work with the new AutoGen 0.4 that is now in main.