QT6 port

Will kstars moving to qt6? So far it requires many old, qt5 packages. Granted, kstars is not the only one, but at some point it will have to move forward.

Currently kstars need those old packages: kplotting5 knewstuff5 knotifyconfig5 qt5-datavis3d qt5-quickcontrols qt5-websockets qtkeychain-qt5