Updater: Add POST_NOTIFICATIONS permission & pre-grant it

Without the permission, Updater can't spawn notifications on
downloads/install

Reference: https://developer.android.com/develop/ui/views/notifications/notification-permission


Test: boot, download an update via updater, check notification drawer
Co-authored-by: Michael Bestas <mkbestas@lineageos.org>
Change-Id: I131c62ae5033f56f8915426f68f7aea76dba78dd