Option to have drag and drop provide an URL instead of, or together with, an image

[Zweibach]

For example for Discord so instead of/in addition to the image being posted the top URL gets posted. Top URL being either just "randomly" defined by Hydrus or using rules set by #550.

It's particularily useful for images/files over the 8MB size limit that normal Discord users have, sharing the original source so people don't get degraded quality copies or have to reverse-search for the source themselves, and so on.