## What problem does this PR solve?
Closes#15021.
The Go model-provider layer had no support for **Azure OpenAI**. Azure
OpenAI is *not* a drop-in base-URL swap of the OpenAI driver — it
differs in authentication, endpoint structure, and how models are listed
— so it needs its own `ModelDriver` implementation.
## Type of change
- [x] New feature (non-breaking change which adds functionality)
Co-authored-by: Jin Hai <haijin.chn@gmail.com>