Gate CDMA Supplementary Services on a CarrierConfig item

Introduce the KEY_SUPPORT_SS_OVER_CDMA_BOOL carrier config, which
allows Supplementary Services to be changed via carrier USSD codes.

This is disabled by default because the current USSD codes are not
configurable per carrier, so it can not be widely enabled.

Bug: 191057045
Test: manual, configuration changes
Change-Id: I3aeb1793c0df4f52764fef5fd09db47efe841dc2