Feature Request: Simplify Integration of Litellm with OpenAI-Compatible APIs

**Describe the solution you'd like**

Litellm is a widely used tool in the AI community that allows deploying a proxy and providing access via HTTP API. Additionally, the Litellm API is compatible with the OpenAI API protocol. It would be beneficial to simplify the process of creating a LitellmModel using the existing implementation available at:
https://github.com/cloudwego/eino-ext/tree/main/libs/acl/openai.

**Additional Context:**
litellm proxy doc: https://docs.litellm.ai/docs/simple_proxy
litellm api: https://litellm-api.up.railway.app/#/