Different upstreams for allow listed domains

If the upstreams themselves block some domains, allow listing them in AGH does not help, the upstreams will still return `0.0.0.0`. E.g. using the AdGuard DNS upstreams (or other filtering upstreams) for the family protection features.

It would be useful to have an optional config in AGH that uses a different upstream for allow listed items so they never get blocked.