Update carrier config for support auto unhold

Deprecate the existing KEY_ALLOW_HOLD_IN_IMS_CALL_BOOL carrier config as
VZW has stated that they support holding. We also need to add a new
carrier config to support carriers that want to allow auto-unholding
the background call for remotely disconnected calls.

Bug: 439893979
Bug: 400808756
Flag: com.android.internal.telephony.flags.support_auto_unhold
Test: atest ImsCallingTest
Change-Id: I02f4d7d98687b8e6ba9d74958e4bb5c8929c5658