Expand the "extra_model_paths" to include other folders

### Feature Idea

The "extra_model_paths" method is a great idea for many reasons. The problem is it's only limited to models and the /models folder.

This feature requests that this be expanded to allow for other folders as dictated by the user. In my use case, the input and output and workflows (user/default/workflows) but other folders could be included also.

### Existing Solutions

My existing solution is to use the Windows feature "symlinks". So all my models, workflows (user/default/workflows), output and input can live outside of ComfyUI's currently installed folder.

IE:
A:/models symlinks to A:/ComfyUIv1.20/models and A:/ComfyUIv1.23/models
A:/input => A:/ComfyUIv1.20/input and A:/ComfyUIv1.23/input
A:/output => A:/ComfyUIv1.20/output and A:/ComfyUIv1.23/output

### Other

Reasons why we need to reference other folders besides "/models":

Many of us have different ComfyUI versions, for whatever reason ie: a certain version worked better in a certain situation, so maybe we have A:/ComfyUI_latest and A:/ComfyUIv0.15.0 or A:/ComfyUI_business and A:/ComfyUI_personal. Whenever anything gets messed up, such as installing certain nodes, and our configuration gets so messed up, it's easier to just install a fresh version of the base Comfy files, ie: main.py, server.py, etc and having to move over thousands of files from /input and /output is a huge hassle and time sink. All the same reasons we wouldn't want to have multiple models in various folders, there is almost always a benefit to having it in one source of truth, ie: A:/whateverfolder

Thanks.

Start by locating the existing extra_model_paths method and inspect the path handling around main.py and server.py. Define how user-specified input, output, and workflows folders should be configured, then verify those folders work without symlinks across the requested use cases.

Written by the indexing model from the issue text.