Add a new trigger which turns LEDs on when there is input
(/dev/input/event*) activity and turns them back off again after there has
been no activity for 5 seconds.

This is primarily intended to control LED devices which are a backlight for
capacitive touch-buttons, such as e.g. the menu / home / back buttons found
on the bottom bezel of many somewhat older smartphones and tablets.

This can also be used to turn on the keyboard backlight LED on input
events and turn the keyboard backlight off again when idle.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20240531135910.168965-2-hdegoede@redhat.comSigned-off-by: Lee Jones <lee@kernel.org>