Add ADAPTIVE_BATTERY_MANAGEMENT_ENABLED

APP_STANDBY_ENABLED is controlled by server side to do experiment.
Before this CL, Adaptive Battery is hooked up to this flag, so
even though if user turns it off, it may be turned on by server.

Add a high level ADAPTIVE_BATTERY_MANAGEMENT_ENABLED to control
the feature in settings UI side.

AppStandbyController looks at both flags and enables standby
only if both are true.

Bug: 78153913
Test: Build
      Manually change both flags (through UI and adb)
      Verify dumpsys usagestats shows the correct state
      for mAppIdleEnabled.
Change-Id: I1fb4461f382e1ee87000fdc38962d94a17891c1e