For most protocols, the operations to manage profiles require a unique
'profile-id' as index. This applies to AT, QMI and generic MBIM.
But for MBIM using the Microsoft Extensions for profile management,
this is no longer true; the device expects the 'apn-type' to be the
index.
This new property lets the user know which is the expected index field
in the Delete() and Set() operations.
This new interface allows modems to expose the list of available
connection profiles stored in the device and edit or delete them; as
long as the underlying device/protocol allows it.