Discover's `--local-filename` flag should support external URIs, too

Considering that

plasma-discover --local-filename file://$HOME/Downloads/naps2-7.4.0-linux-arm64.flatpak

works, I’m surprised that

plasma-discover --local-filename

doesn’t — I’m aware that it’s local-filename rather than external-filename or merely filename, but it’d be massively more convenient for it to be able to get packages this way too.

sudo zypper install

allows it.