[Android] Add ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS as an option to obtain excemption from battery optimizations

[JulianAssmann]

On android, add ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS as an option to obtain excemption from battery optimizations, as declaring REQUEST_IGNORE_BATTERY_OPTIMIZATIONS might lead to a ban of the app in the Play Store, "unless the core function of the app is adversely affected" (see the note here)

[datdescartes]

@JulianAssmann As option to not request battery optimization permission is added, could you release new version to pub.dev? The current version(1.1.0) doesn't reflect latest code

[JulianAssmann]

@datdescartes Release 1.2.0 should now incorporate these changes :)