### What problem does this PR solve?
Implement OpenAI chat completions in GO
POST /api/v1/openai/<chat_id>/chat/completions
OpenAI chat cli: internal/development.md
### Type of change
- [x] Refactoring
### What problem does this PR solve?
Use GetChatModel, remove duplicate functions in model_service.go
### Type of change
- [x] Refactoring
Co-authored-by: Jin Hai <haijin.chn@gmail.com>