Allow uploading a file via a web URL

[SuperKael]

is your feature request related to a problem? Please describe.
When transferring files between two online services, it can take much longer than theoretically necessary due to needing to first download the files from one service, and then upload them to another.

Describe the idea / solution you'd like
Allow 'uploading' a file by providing a URL, which copyparty would then download directly from, without the file ever passing through the machine of the user initiating this action. I.E., the user simply pastes a URL like https://example.com/file, and copyparty downloads the file located at that URL.

Describe any alternatives you've considered
Naturally there's always the option of the user downloading the file themselves, then uploading it to copyparty, however this is liable to take orders of magnitude longer, particularly since consumer internet service (in America, at least) often provides drastically lower upload bandwidth than download.

[icxes]

This is sort of possible through the use of hooks, such as the wget hook. You can POST urls to a volume with this active and have copyparty directly download it. One way of doing this through the UI itself is to just to paste an url on the "send message to server log" thing that appears when you click the 📟 icon, but you could just as well use curl or any other tool. Admittedly, the UX of this one is kinda poor since there's no progress or failure indicators...

For the record, enabling it in your config would be something like this:

[/uploads]
  /mnt/some/example
  accs:
    (whatever you have here)
  flags:
    xm: f,j,aw,t300,/filesystem/path/to/wget.py