Add support for DeepSeek API

[sevenjay]

Describe the need of your request

CodeGPT could integrate with the DeepSeek API to enhance its capabilities in coding. The DeepSeek Coder V2 (236B) model gets the top score on aider’s code editing benchmark. https://aider.chat/docs/leaderboards/ DeepSeek API Doc https://platform.deepseek.com/api-docs/

Proposed solution

No response

Additional context

No response