Pull request: 5035-dhcp-hosts-netip-addr

Updates #5035.

Squashed commit of the following:

commit 3a272842f738da322abb2bc5306aed94da79304b
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Oct 26 20:34:49 2022 +0300

    dnsforward: imp docs, tests

commit b442ca9b57d730be3af14c68759c706f1742e4c4
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Oct 26 19:51:21 2022 +0300

    dnsforward: imp code, tests

commit 8fca6de93edb8cfdb0ff5a940d08f8700e12a423
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Oct 26 16:38:27 2022 +0300

    dnsforward: mv dhcp hosts to netip.Addr

internal/aghtest/aghtest.go

@@ -10,6 +10,8 @@ import (
 )
 
 // DiscardLogOutput runs tests with discarded logger output.
+//
+// TODO(a.garipov): Replace with testutil.
 func DiscardLogOutput(m *testing.M) {
 	// TODO(e.burkov): Refactor code and tests to not use the global mutable
 	// logger.