Adding a custom OpenAI endpoint

[GreenShadeZhang]

Add custom openai endpoints to adapt to more large models compatible with the openai api interface. If the endpoint is not configured, it will not affect the original function.

[Joannall]

got error after merge

[GreenShadeZhang]

got error after merge

   {
     "Provider": "openai",
     "Models": [
       {
         "Name": "qwen2.5-72b-instruct",
         "ApiKey": "***",
         "Endpoint": "https://dashscope.aliyuncs.com/compatible-mode/v1/",
         "Type": "chat",
         "PromptCost": 0.0015,
         "CompletionCost": 0.002
       }
     ]
   }

Here's an example configuration of the other large models I use that are compatible with the OpenAI interface. If you don't want to customize the endpoint, don't write the endpoint field.