livesys-kde: Enable Plasma Welcome for live environments with Plasma 6
    
    Starting with KDE Plasma 6, there is support for welcoming a user
    into the new live environment and guiding them to install the
    operating system.
    
    This attempts to be a backward compatible change with the previous
    KDE Plasma 5 logic of disabling the welcome wizard entirely when
    live session support does not exist.