Add QXMPP
needed for Kaidan
- Android Qt 5 already there: https://invent.kde.org/plata/ci-images/-/blob/master/android-qt515/CI-Craft-Packages.list#L61
- Android Qt 6 in !106 (merged)
- Linux Qt 5 added and checked that image builds locally
- Linux Qt 6 prepared but doesn't build (chooses Qt 5)
- Windows Qt 5 and Qt 6 added but didn't check if images build