[feat, Kobo] Autoshutdown (#5335)

The methods used here will likely work on most embedded devices, which is why I put them in their own WakeupMgr interface/scheduler module, separate from Kobo.

See https://www.mobileread.com/forums/showthread.php?p=3886403#post3886403 for more context.

Fixes #3806.

frontend/ui/elements/reader_menu_order.lua

@@ -61,6 +61,7 @@ local order = {
         "time",
         "battery",
         "autosuspend",
+        "autoshutdown",
         "ignore_sleepcover",
         "ignore_open_sleepcover",
         "mass_storage_settings",