Add flag to control changes to disable contacts syncs in clone

Adding a device config flag inside app_cloning namespace
to gate the building blocks added in the U release, indcluding contact
sharing.

Turn the flag on: adb shell device_config put app_cloning
enable_app_cloning_building_blocks true

Turn the flag off: adb shell device_config put app_cloning
enable_app_cloning_building_blocks false

Bug: 253449368
Test: atest SyncManagerTest
Change-Id: Ieb5c3567f599b4f9166443d0c3bca970dba51d9f