Pull request 2076: 1660-disable-plain

Updates #1660.

Squashed commit of the following:

commit d928a00b7c77a33717fe3e77aace1f1b41a960d2
Merge: 38e401d78 0f5e8ca56
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Nov 22 13:39:34 2023 +0300

    Merge branch 'master' into 1660-disable-plain

commit 38e401d7827ce1ea190b5328cadb3bb0ff5a5cba
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Nov 21 20:17:53 2023 +0300

    dnsforward: imp validation

commit f9e99cec209078128fef1b147294c7abe3f6ae70
Merge: cb7529682 c8f1112d4
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Nov 20 16:02:31 2023 +0300

    Merge branch 'master' into 1660-disable-plain

commit cb75296821cae594e8c4d17dfdd8be2190aee7f7
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Nov 17 14:20:02 2023 +0300

    all: add serve_plain_dns

CHANGELOG.md

@@ -25,10 +25,14 @@ NOTE: Add new changes BELOW THIS COMMENT.
 
 ### Added
 
+- Ability to disable plain-DNS serving through configuration file if an
+  encrypted protocol is already used ([#1660]).
 - Ability to specify rate limiting settings in the Web UI ([#6369]).
 
 #### Configuration changes
 
+- The new property `dns.serve_plain_dns` has been added to the configuration
+  file ([#1660]).
 - The property `dns.bogus_nxdomain` is now validated more strictly.
 - Added new properties `clients.persistent.*.upstreams_cache_enabled` and
   `clients.persistent.*.upstreams_cache_size` that describe cache configuration
@@ -40,6 +44,7 @@ NOTE: Add new changes BELOW THIS COMMENT.
 - Pre-filling the New static lease window with data ([#6402]).
 - Protection pause timer synchronization ([#5759]).
 
+[#1660]: https://github.com/AdguardTeam/AdGuardHome/issues/1660
 [#5759]: https://github.com/AdguardTeam/AdGuardHome/issues/5759
 [#6369]: https://github.com/AdguardTeam/AdGuardHome/issues/6369
 [#6402]: https://github.com/AdguardTeam/AdGuardHome/issues/6402