Replace background thread executions with the Utility QoS

[ChrishonWyllie]

Why: performing tasks on the background thread may never run if the device is in low power mode.

Check out these posts/articles:

• https://twitter.com/gregheo/status/1001501337907970048?lang=en
• https://developer.apple.com/library/archive/documentation/Performance/Conceptual/EnergyGuide-iOS/PrioritizeWorkWithQoS.html