Pull request: all: improve dnsrewrite handling

Merge in DNS/adguard-home from 2491-dnsrewrite-log to master

Closes #2491.

Squashed commit of the following:

commit bfe3cb599ed0a921285fb1a6ea27aaefdcc0d093
Merge: 95c5ffe43 15d8f979b
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 28 18:33:32 2020 +0300

    Merge branch 'master' into 2491-dnsrewrite-log

commit 95c5ffe4360b732556455f24b844dad27047e64b
Author: Artem Baskal <a.baskal@adguard.com>
Date:   Mon Dec 28 18:11:01 2020 +0300

    Add RewriteRule for client

commit b9096c8789009dac1838b542d3409fef54b59aa5
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 28 17:22:44 2020 +0300

    all: imp naming, docs

commit 4e00de0d613e4740451e4c8eb5a1de35a70a5896
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 28 17:16:35 2020 +0300

    all: imp naming, add todo

commit 67e4045f627a9569f382309705963640dcf3454a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 28 16:53:00 2020 +0300

    all: improve dnsrewrite handling

internal/dnsforward/dns.go

@@ -366,8 +366,8 @@ func processFilteringAfterResponse(ctx *dnsContext) int {
 	var err error
 
 	switch res.Reason {
-	case dnsfilter.ReasonRewrite,
-		dnsfilter.DNSRewriteRule:
+	case dnsfilter.Rewritten,
+		dnsfilter.RewrittenRule:
 
 		if len(ctx.origQuestion.Name) == 0 {
 			// origQuestion is set in case we get only CNAME without IP from rewrites table