Update battery saver schedule min trigger value

- Udpate the min value to 10%, also change related preference summary
   and seekbar value
 - Make battery saver main page's switch support first time trigger
   warning

Bug: 207470943
Test: make RunSettingsRoboTests
Change-Id: I120b9a6784ed90eacccb09bb11f079f12679e95c

src/com/android/settings/fuelgauge/batterysaver/BatterySaverButtonPreferenceController.java

@@ -111,9 +111,8 @@ public class BatterySaverButtonPreferenceController extends
 
     @Override
     public boolean setChecked(boolean stateOn) {
-        // This screen already shows a warning, so we don't need another warning.
         return BatterySaverUtils.setPowerSaveMode(mContext, stateOn,
-                false /* needFirstTimeWarning */);
+                true /* needFirstTimeWarning */);
     }
 
     @Override