[Forensic] Add BackupTransportConnector

The ForensicService uses the BackupTransportConnector
to send commands to the BackupTransport binder service.
Three commands are as following:
1. Initialize
2. AddData
3. Release
The BackupTransportConnector is also in charge of
bind and unbind the BackupTransport binder service.

The config_forensicBackupTransport is used to specify
the BackupTransport binder service. It's empty on AOSP.
GMS overlay file will include a BackupTransport binder
service on GMS Core for GMS devices.

Bug: 365994454
Test: atest ForensicServiceTest
Flag: android.security.afl_api
Ignore-AOSP-First: security feature

Change-Id: Ib40f9b0ba2655a9c1fc4de0a104211661082086a