Added flag to enable subscription manager service through adb

Test: Boot up and basic phone testing
Test: adb root && adb shell device_config put telephony enable_subscription_manager_service true
      && adb shell device_config set_sync_disabled_for_tests persistent && sleep 3 && adb reboot
Fix: 266896752
Merged-In: I14ff642402929bcfd39e6c20c50588ef8eec4eed
Change-Id: I14ff642402929bcfd39e6c20c50588ef8eec4eed