Add support for respecting macOS "Low data mode"

[fnwbr]

Auto updates should respect the host system indicating that it wishes to pause auto updates. Users might enable this mode when they're running on a metered connection, for example.
Apple added this toggle with macOS 10.15 Catalina: https://support.apple.com/en-bn/guide/mac-help/mh11935/mac

Official documentation:

• https://developer.apple.com/documentation/foundation/nsurlsessionconfiguration/3235751-allowsconstrainednetworkaccess

Also see:

• https://www.donnywals.com/supporting-low-data-mode-in-your-app/