Add options for `network.enabled` and `network.error`

[toddhgardner]

Add options to match the TrackJS Browser agent by installing with:

TrackJS.install({
   token: '',
   network: { enabled: true, error: true }
});

enabled toggles whether or not we should record network requests in telemetry automatically. error toggles whether an error should be recorded if the network request returns with a >=400 status code.