Opportunistic Sub Grouping Keys in CarrierConfig

Add two keys to allow new subscriptions to be added
into subscription groups before carrier config changes
are broadcast.

Bug: 123721160
Test: atest SubscriptionInfoUpdaterTest
Merged-In: Ib6f811b70e41eba897b9bde0c0aeb0c880169f66
Change-Id: Ib6f811b70e41eba897b9bde0c0aeb0c880169f66
(cherry picked from commit c24e219f)