希望能；添加一个自动备份功能

### Please make sure of the following things

- [X] I have read the [documentation](https://alist.nn.ci).
- [X] I'm sure there are no duplicate issues or discussions.
- [X] I'm sure this feature is not implemented.
- [X] I'm sure it's a reasonable and popular requirement.

### Description of the feature / 需求描述

现在网盘都有自动备份功能，我觉得这个很实用，如果可以的话能指定备份目录直接同步到Alist里面管理的网盘就好了，可以检测到文件夹的变动然后实现自动备份这样的功能。

### Suggested solution / 实现思路

_No response_

### Additional context / 附件

_No response_