[.Net] Add Ollama Support

[mikelor]

Why are these changes needed?

Added support for Ollama. Ollama allows you to run Llama 3, Phi 3, Mistral, Gemma, and other models locally.

This is basic support and utilizes Ollama's OpenAI compatibility. More robust support can be added in a future release. The current model is heavily based on Azure's OpenAI service. I'd be happy to collaborate on a reviewing a future implementation that allows support for more LLM hosting options, and specifics.

Related issue number

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.

[mikelor]

@microsoft-github-policy-service agree