Adding flag for new carrier config.

Adding support for configuring whether a carrier wants to log "calls answered elsewhere" in the call log.  This applies for multiendpoint type solutions where a call rings on multiple devices at the same time.

Test: Added new unit test to cover this functionality.
Flag: com.android.internal.telephony.flags.log_calls_answered_elsewhere
Bug: 405460896
Bug: 432782589
Change-Id: Iaff1a915a9e774f51b25de58b37ad61fbadb566c