[Feature request] Fetch patch(es) from url

Hey @ds300

Thanks for creating and maintaining `patch-package`, it has made my life much easier 👍

### The Problem

I often find myself copy pasting patches from a codebase to another. While not a huge issue, it would be nice to avoid it.

### Possible Solution

Instead of specifying the package name or git commit the user would provide a url pointing to where the patch is located.

`patch-package` would detect that it's a url, download the patches locally and then work as it does normally.

Is this something you would be interested to add ? Happy to take a shot at a PR if you are !

Cheers