Support vllm-omni to enrich multi-modality generations

### 🚀 Feature Description and Motivation

vllm omni has been released in last Nov, image editing and image generation already have very standard interfaces and solid model integrations. AIBrix should integration with vllm-omni to support such cases.

- [ ] vllm-omni x AIBrix integration samples
- [ ] opportunity to leverage kvcache for vllm-omni
- [ ] aibrix-gateway potential changes for adaptation and payload compatibility

### Use Case

image/video generations.

### Proposed Solution

_No response_