Pull request: 5117-backport-dns64

Merge in DNS/adguard-home from 5117-backport-dns64 to master

Updates #5117.

Squashed commit of the following:

commit 8ac88534b2da52f49facef6d623ea3504a3cd5ed
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Feb 6 16:44:16 2023 +0300

    all: rm todos

commit 0aa66c5ecbadc3e372478ea4446f80fcc7457841
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Feb 6 15:40:38 2023 +0300

    all: upd dnsproxy

commit 872a8efdd2759fd9dad61de9953bc87f734ca918
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Feb 3 14:14:21 2023 +0300

    dnsforward: imp docs

commit 8efeb42cac69bbe9b8dba8c91c33b14c95397ab9
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Feb 1 02:58:01 2023 +0300

    all: rm dns64

internal/dnsforward/dnsforward_test.go

@@ -89,9 +89,14 @@ func createTestServer(
 	s.serverLock.Lock()
 	defer s.serverLock.Unlock()
 
+	// TODO(e.burkov):  Try to move it higher.
 	if localUps != nil {
-		s.localResolvers.UpstreamConfig.Upstreams = []upstream.Upstream{localUps}
+		ups := []upstream.Upstream{localUps}
+		s.localResolvers.UpstreamConfig.Upstreams = ups
 		s.conf.UsePrivateRDNS = true
+		s.dnsProxy.PrivateRDNSUpstreamConfig = &proxy.UpstreamConfig{
+			Upstreams: ups,
+		}
 	}
 
 	return s