discover-backend-flatpak from KDE:Frameworks5 project

需要 openSUSE Leap 15.6 ，用 root 執行：

zypper addrepo https://download.opensuse.org/repositories/KDE:Frameworks5/openSUSE_Leap_15.6/KDE:Frameworks5.repo
zypper refresh
zypper install discover-backend-flatpak