添加一个路径映射存储

### 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

需求
/volume/aliyun # 挂载的aliyun盘
/volume/189pan # 挂载的189盘

如果我想在 189pan的基础下 挂载一个新的盘
/media 挂载到 /volume/189pan/media
可以通过"别名"实现 但是有缺陷 不能上传

这个功能很有必要(不用添加多个相同的存储来实现挂载不同路径的功能)

谢谢 Alist开发者

### Suggested solution / 实现思路

_No response_

### Additional context / 附件

_No response_