Add a setter for the B&R logger in SettingsHelper.

I'm doing this change so that the logger can be accessed in SettingsHelper as an internal variable instead of having to pass it as an argument in all the methods that need logging.

Bug: 379861078 
Change-Id: I34b22b4b267f2376f657efbbb7fee7f37ab0c905
Flag: com.android.server.backup.enable_metrics_settings_backup_agents
Tested: SettingsHelperTest