Always show distro name for PackageKit apps

Discover tries to show the name of the repo that an app comes from. This string is generally human-readable for Snap, Flatpak, KNS, and even apps from 3rd-party PackageKit repos. But it is usually not human-readable for apps that come from distro repos, because it's common for distros to ship multiple repos that serve different purposes. When we try to show the name of these repos in the UI, it's nonsense; we end up with text like "Distributed by: xenial-security universe" and Distributed by: updates". This text doesn't make any sense to the user and can even be scary; imagine "Distributed by: Restricted" which is what you can see on Ubuntu-based distros!

The user does not care about which specific distro repo the app comes from; what they care about is that it came from their distro.

What would be ideal is if PackageKit could tell us whether a particular PackageKit repo was 1st-party or 3rd-party. Then for 3rd-party repos we could show the actual name (which usually ends up looking reasonably human-readable, like "Packman" or "rpmfusion-free"), and for 1st-party repos, we could instead substitute the distro name.

Unfortunately PackageKit doesn't have that functionality right now. See https://github.com/PackageKit/PackageKit/issues/607.

So for now, just show the distro name for all PackageKit apps. This fixes the nonsense strings issues, and while it does result in inaccuracy for users who have installed 3rd-party package repos, those users are generally technically knowledgeable enough to understand.

BUG: 465204 FIXED-IN: 5.27.2

(cherry picked from commit 5b23cca9)