[wireguard-ios] Allow user to specify the value of dnsSettings.matchDomains in func generateNetworkSettings()

[Chandler Ding]

Dears Roopesh & Jason,
  Wireguard ios client works perfectly for me, thanks for the great work.
  Here is a feature request, instead of resolve all domain via tunnel's dns server, users may only need resolve particular domains.
  Could you kindly consider allow end user to specify the value of dnsSettings.matchDomains in func generateNetworkSettings() so that no all dns resolve goes via tunnel dns servers.
 Best Regards & Many thanks.