[SUBID01-0]Grow NetworkIdentity to include a new mSubId field

In the previous design of NSS and NPMS, those only had IMSI to identify
the cell network. Now the telephony has created the "subId" handle,
which is the preferred mechanism for identifying subscribers.

This commit adds NetworkStats support for subscriberId as a part of
the network identity key

Bug: 80526261
Test: atest NetworkTemplateTest NetworkStatsCollectionTest
            NetworkStatsServiceTest NetworkIdentityTest
            NetworkStatsDataMigrationUtilsTest
Change-Id: Ie1fe81006555dbcca4b62457fa6c319f04b4576d