postmarketos-base: conditionally cancel suspend with elogind

This is an attempt to implement the 'short term' solution described here: #843 (comment 436873580)

TODO:

• Once a suspend is canceled by the hook, elogind doesn't try to suspend the system again. It should try again after the amount of idle time has been surpassed (again)
  • it looks like it tries again if elogind sees action in the session (e.g. display is woken up, UI interaction takes place). Is this good enough?
  • EDIT: This is good enough for now
• /lib/apk/db/lock doesn't actually get cleaned up by apk, so another test is needed for determining if apk is active (pgrep for process, or ??)
  • apk doesn't create/remove this file, it gets an exclusive lock on it, so the hook uses lslocks to check this condition.
• Anything else to block suspend on? Not sure if music players, etc can be added to this..
  • EDIT: No, will do follow up MR for anything else that comes along