Hook up bt related knobs to AnomalyDetectionPolicy

This cl adds the following knobs:
1. bluetoothScanDetectionEnabled: whether to enable this detector
2. bluetoothScanThreshold: threshold about bt unoptimized scanning
time in background

Also add the default values for these knobs, which are:
1. bluetoothScanDetectionEnabled: true
2. bluetoothScanThreshold: 30 minutes

Bug: 36921532
Test: RunSettingsRoboTests
Change-Id: I7619453ebe3cc3f5a13b3bbd4fbf3b65a1f1d45c