Add option to set custom OpenAI API URL

[stone2401]

In the current technological environment, it is essential for applications to support the integration of multiple models. This enhances the flexibility and scalability of the applications, allowing them to adapt to the ever-changing technological and user needs. I have made some modifications to the original code to support the integration of other models. These modifications might affect some parts of the original code, and I am not sure if this would be a concern.