Surface more alt stores besides flathub

### Problem

The concept of alt stores and flatpak remotes still seems to be a bit confusing, especially when we currently only suggest a single alt store

### Proposal

We should show many alt stores to make it more clear that there is a variety of remotes to get apps from. Just briefly:

http://distribute.kde.org/kdeapps.flatpakrepo
https://nightly.gnome.org/gnome-nightly.flatpakrepo
https://flathub.org/repo/flathub.flatpakrepo

There is also a Fedora remote and one for OnePassword, but I'm having trouble finding the links to the repo files

### Prior Art (Optional)

_No response_