Create REGISTER_STATS_PULL_ATOM permission

Create a permission to allow clients to register pull atom callbacks to
statsd. This permission should allow mainline modules and other platform
clients register puller callbacks, but is not intended for 3p apps.

Bug: 146462168
Test: atest CtsPermission2TestCases
Change-Id: Iea50d137e2cc9f34644c8aa9548a7445f5ec16b8