Add GUI Method Of Changing & Adding Model Directories

### Feature Idea

Add a in-GUI method of easily using a OS' native GUI file explorer to search for the directories for already downloaded models directories and not rely basically solely on the editing "extra_model_paths.yaml" end-user unfriendly method currently recommended by ChatGPT and others.

### Existing Solutions

Using the "extra_model_paths.yaml" is **_not_** user friendly and fails miserably unless you understand how to do all the steps without making any user errors based on the limited documentation currently available.

### Other

This is just one of the many many reasons people make fun of ComfyUI not being user friendly and hard to learn. After all what's the point of making a GUI if everything is still CLI or aimed at being very expert computer user centric design? As flexibility isn't really much of an excuse at this point in ComfyUI's long life.

Also, seriously add simpler instructions on how to do this if "extra_model_paths.yaml" is _still_ going to be the default/standard method going forward.

Examples of a fix that was recommended:
https://www.reddit.com/r/StableDiffusion/comments/1896top/extra_model_pathsyaml_for_comfy_ui/