Add a field for transport properties to RestoreSet object

Android Framework needs to know for each RestoreSet provided by
BackupTransport the properties of the transport (e.g. device-to-device
transport, encryption) that was used to obtain the data in the restore
set in question.

Bug: 182986784
CTS-Coverage-Bug: 183441953
Test: atest FullBackupRulesHostSideTest
Change-Id: I07bc2d4eb3837390ea3b0aee769d143ab153335d