Support DeepSeek as a LLM Provider

[can-gaa-hou]

Hi maintainers👋,

There was an earlier implementation in PR #6, which DeepSeek was added but later removed. Can we re-support it as a LLM provider? I know GPT and Claude are strong enough in code generation, but they are restricted in some region. Besides, Deepseek is much cheaper compared to them. Lastly, Deepseek uses an OpenAI-compatible API, which means we don't need to refractor the code.

Happy to hear your feedbacks.

cc @sijiac @Laurawly

[Jack-Khuu]

Seems reasonable, let's give it a try