Add a gamingModeEnabled bool and a gamingDismissHintEnabled bool to
the shell settings plugin, persisted in plasmamobilerc [General],
following the same pattern as convergenceModeEnabled.
Two new quick settings tiles:
- org.kde.plasma.quicksetting.gaming: toggles gaming mode on/off,
shows explicit on/off label matching the convergence tile style.
- org.kde.plasma.quicksetting.gaminghint: shown while gaming mode
is active; dismisses the Game Center hint.
Both tiles are added to the default group in quicksettings config.
