Added a command to return app_standby_enabled

The only way to know the runtime state was check dumpsys usagestats, and
parse through a lot of output.
This makes it easier to retreive the state.

Test: adb shell settings put global app_standby_enabled 0
adb shell dumpsys usagestats is-app-standby-enabled

Bug: 74336662
Change-Id: Ibe80d27bdf940682b9e4c3c14f93b4871f9f1746