[Spike] Look into available network information on various platforms

This spike complements QTBUG-86966.

The purpose of this spike is to figure out what sort of APIs are available on various platforms and potentially how is it accessed (e.g. which platform has API to get metering info). And to see in general if there is additional information some platforms may have available that would be useful to provide access to (if it makes sense from a cross-platform perspective), example:
macOS has their Reachability framework where you can ask specifically "when is host 'X' available" which then notifies you when it's available, presumably this is also optimized to be queued along with bursts of work across the OS to save power. Could we reasonably replicate this across other platforms or is there similar API available?