iframe 预览增加基础变量

### Please make sure of the following things

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

### Description of the feature / 需求描述

需求来源: `nbviewer` 在线预览 notebook, 其会使用这样的地址: *https://nbviewer.org/urls/* 后加无 protocol 的文件地址, 如: *https://nbviewer.org/urls/wdav.a.cn/p/local/test.ipynb*

期望增加一个基础变量: 地址不包含 url protocol (也就是 http/https) 的变量。
例如: `no_protocol _url` 会将 *raw_url='https://dav.a.cn/p/file1'* 转变为 *'dav.a.cn/p/file1'*

https://github.com/alist-org/alist-web/blob/8671473111c2391b9d2abc6989fcc16cff60733d/src/utils/str.ts#L59

### Suggested solution / 实现思路

_No response_

### Additional context / 附件

_No response_