Move Settings backup and restore metric logging from SettingsProvider to SettingsHelper

This moves the logging of backup and restore related metrics to SettingsHelper where the database restore actually happens. For now, I added logging when the values are written into the database. I'll handle other cases in future CLs.

Change-Id: I2752aa3b84a431c26005a8796c1d79ab5d54d8d7
Bug: 379861078
Flag: com.android.server.backup.enable_metrics_settings_backup_agents
Tested: SettingsHelperTest