Add containment switcher to wallpaper dialog

Add a containment switcher, taken directly from https://invent.kde.org/plasma/plasma-desktop/-/blob/master/desktoppackage/contents/configuration/ConfigurationContainmentAppearance.qml

sidenote: I wonder if it would make sense to just add the shell configuration into Plasma Mobile to improve the wallpaper switcher for touch, these aren't even used by Bigscreen (it already has its own thing...)