Support alternative OpenAI hosts

[pamelafox]

To make the sample more accessible, could you support all or some of:

• OpenAI.com models - See https://github.com/pamelafox/python-openai-demos for example
• GitHub models - See https://github.com/pamelafox/python-openai-demos for example
• Ollama models

See my tips here for Ollama compatibility (the hardest of the list!)
https://blog.pamelafox.org/2024/08/making-ollama-compatible-rag-app.html