Add basePath configuration option to support OpenAI mirror

[try-to-fly]

This pull request is aimed at adding a new configuration option, basePath, to the project. This is motivated by the need to support an OpenAI mirror site in China. (such as https://api2d.com/)

The basePath will allow users in China to conveniently redirect their requests to a local mirror, thus significantly improving access speed and reliability.

Please consider integrating this change to enhance the user experience for a large number of users in China.

[CLAassistant]

All committers have signed the CLA.

[HenryHengZJ]

@try-to-fly can you add the same to OpenAI node as well?

[try-to-fly]

@try-to-fly can you add the same to OpenAI node as well?

I have also added the basePath setting to the OpenAI_LLMs node。

[HenryHengZJ]

thanks @try-to-fly!