Add POST_NOTIFICATIONS permission to DLC and kiosk app roles.

Bug: 285213134
Test: permission granted

adb shell dumpsys package com.google.android.devicelockcontroller
shows that the permission is granted to DLC.

adb shell dumpsys package com.google.android.apps.sample.kioskvnext
shows that the permission is granted to the kiosk app.

Change-Id: I6590c1187e0d73d8ed7f9022466ce9eb780c86aa