[Feat]: Add `disable-folder-downloads`

## What is your suggestion?
1. `disable-file-downloads` prevents all forms of downloading
2. I would like to disable downloading of whole folders only but allow downloading of 1 file

## Why do you want this feature?
My aim is to not allow whole folder downloads as it can lead to bad practices/security issues but downloading of files, 1 by 1 is acceptable as a convenience feature

## Are there any workarounds to get this functionality today?
Yes, allow file downloads which also allows folder downloads

## Are you interested in submitting a PR for this?
Unfortunately no as my javascript is subpar.

首先找到现有的 `disable-file-downloads` 设置，以及处理文件夹下载的代码路径。确认单个文件下载与整个文件夹下载的区别，然后更新设置行为，使文件夹下载被阻止，同时仍允许单个文件下载。

由索引模型根据 Issue 内容生成。