since #5984, add DeepSeek as a new ModelProvider (with deepseek-chat&deepseek-coder models), so that user can use openai and deepseek at same time with different api url & key

since #5984, add DeepSeek as a new ModelProvider (with deepseek-chat&deepseek-coder models), so that user can use openai and deepseek at same time with different api url & key #930