[Suggestion] add distrobox backend to discover

[bojogon7]

Is your feature request related to a problem? Please describe.
You need to go to separate program to update install software from distrobox. And no GUI for searching packages with support for AppStream

Describe the solution you'd like
Add Distrobox backend to discover.

It could work like:

1. Search package on debian 13 system
2. It searches packages from Distrobox and Debian 13
3. You get to choose which package to get like you can choose from system repository and flatpak with flatpak backend
4. You can for example install packages from Debian 13 and Debian unstable from discover

Describe alternatives you've considered
Consider if it is feasible

Additional context
https://apps.kde.org/discover.packagekit/

You could install up to date software on Debian 13 from Debian sid repository on Distrobox.