ComfyUI api ability to pass a "subfolder" parameter to server "/prompt" route

### Feature Idea

I am currently trying to implement ability to render to subfolders (ComfyUI/output/subfolder-name)

When I trigger a prompt - I cant seem to specify a parameter to tell comfy that i want the output to be at a specific subfolder. It always dumps them in the output folder

### Existing Solutions

none that i know of - not even examples

### Other

my frontend is just a react app using a fetch post request. I cant seem to figure out how to tell comfy to even pass data from the frontend to it. Example
https://github.com/blurymind/cozy-fireplace/blob/main/__init__.py