Add Backup & Restore Metrics for lock settings.

Bug: 379861078 
Flag: com.android.server.backup.enable_metrics_settings_backup_agents
Tested: Tested manually, as lock settings don't have tests currently and I couldn't find a way to test this without major infra changes.
Change-Id: I8a7319a97f0f9d2c2bf5e556d66e38f70acbf9a9