dify support

[iamsk]

And, you don't need to implement other llms.

[kennymckormick]

Hi, @iamsk,
Thanks for helping to implement DifyVision API in VLMEvalKit. Some further steps are required to be accomplished before merging:

1. I cannot find any information about DifyVision on the Internet, a modelcard that introduce the API model is required.
2. Since we do not own a key of DifyVision, please share us a key (with small amounts of quota) for verification.
3. The content of the PR should be modified: demo.py should be removed from the PR.
4. Please follow the development guide (https://github.com/open-compass/VLMEvalKit/blob/main/Development.md) last section to format your code.

[kennymckormick]

Hi, @iamsk ,
Is there any updates? Just a kind reminder.