add support for `systemctl suspend-then-hibernate`
Context: recent versions of systemd introduced a new option for sleeping, "suspend then hibernate". It will suspend the machine (to RAM), but after a certain timeout, automatically wake the machine from sleep and immediately hibernate it.
This limits the maximum time your computer is in sleep mod, and thus limits maximum power consumption. If you wake up your computer soon enough, however, the operation will be quick as the computer didn't go into deep sleep yet.
Please add this option into Settings Manager > Power Manager > General > Buttons > When *** is pressed ?