Expose grouping and opportunistic carrier config keys.

These have been fully functional since Q, but were not a part of the
public API at that time. This makes the keys public with a note that
they'll work all the way back to Q (API 29).

The security concern has been resolved in b/181053462.

Fix: 130676550
Test: m update-api && m offline-sdk-docs && m -j
Change-Id: Ie2e4370999d48543517346e933ac35f6d298a127