Azure support for demo UI?

I see that #131 and #134 added Azure support to sycamore. Apparently the demo does not support this yet; at least all the documentation just mentions setting `OPENAI_API_KEY`.

I can see that the OpenAI proxy code in demo-ui just hardcodes the endpoint: https://github.com/aryn-ai/sycamore/blob/f5653f7cf8abd10e793abf36920dccaf8a8d6d11/apps/demo-ui/openai-proxy/py_proxy/proxy.py#L40