Pull request: 4865-refactor-dns-handlers

Updates #4865.

Squashed commit of the following:

commit b874088ee72dfd0cae5f4102fac87e1f26245ddf
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Sep 2 14:01:52 2022 +0300

    dnsforward: imp code, docs

commit a1b95fda58b777a54e7dcd57f0c419200f8fdc15
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Sep 1 19:37:45 2022 +0300

    all: refactor dns handler; opt

internal/querylog/qlog_test.go

@@ -271,13 +271,13 @@ func addEntry(l *queryLog, host string, answerStr, client net.IP) {
 	}
 
 	res := filtering.Result{
-		IsFiltered:  true,
-		Reason:      filtering.Rewritten,
 		ServiceName: "SomeService",
 		Rules: []*filtering.ResultRule{{
 			FilterListID: 1,
 			Text:         "SomeRule",
 		}},
+		Reason:     filtering.Rewritten,
+		IsFiltered: true,
 	}
 
 	params := &AddParams{