Add support provider dify.ai

[Tommy]

Validations

• I believe this is a way to improve. I'll try to join the Continue Discord for questions
• I'm not able to find an open issue that requests the same enhancement

Problem

The dify.ai is not compatible with continue.dev

Dify.ai is a great provider and an easy tools to construct chatbot : https://github.com/langgenius/dify
https://docs.dify.ai/user-guide/launching-dify-apps/developing-with-apis

Solution

Add compatibility to https://github.com/langgenius/dify

[Nate Sesti]

Looks like a great project. As I probably won't get to this immediately over some pressing issues, do you have any interest in making a PR to add this feature? There is a good tutorial of how to do this in CONTRIBUTING.md