Post notification on abusive background current drain

Tapping on the notification will bring up the individual abusive
app's battery settings page. It won't be re-posted after being
dismissed until next day, in order to avoid from spamming the user.

Bug: 200326767
Bug: 203105544
Test: FrameworksMockingServicesTests:BackgroundRestrictionTest
Test: Manual - adb shell am set-bg-abusive-uids & verify notification
Change-Id: I0b30014d748863c66c3845b5f310948a9493e302