feat: Add API Docs and Improve Inference Readability (kaito-project#331)

**Reason for Change**:
This change adds plenty more documentation and OpenAPI spec for our
inference. It also enables the use of preferred non-NVIDIA nodes without
crashing.

**Requirements**

- [x] added unit tests and e2e tests (if applicable).

**Issue Fixed**:
Fixes kaito-project#321 

**Notes for Reviewers**: