Pull request 2174: 6820 Warn local ptrs

Squashed commit of the following:

commit c2319658a49eb750c9c362632697c481ff560c71
Merge: c6162a211 bcd143068
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Mar 14 18:10:20 2024 +0300

    Merge branch 'master' into 6820-warn-local-ptrs

commit c6162a211b96e220271383bd8c84e87ad44ba7f8
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Mar 13 19:35:20 2024 +0300

    dnsforward: fix doc

commit c6cce9644e629a085f3b66cac503e9de0bc9b753
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Mar 13 19:19:49 2024 +0300

    all: fix private conf fail on start

commit c11fc3e7abcd4f592d44a3c163b554017eb305a0
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Mar 13 18:43:31 2024 +0300

    WIP

CHANGELOG.md

@@ -30,6 +30,15 @@ NOTE: Add new changes BELOW THIS COMMENT.
 - Ability to define custom directories for storage of query log files and
   statistics ([#5992]).
 
+### Changed
+
+- Private RDNS resolution (`dns.use_private_ptr_resolvers` in YAML
+  configuration) now requires a valid "Private reverse DNS servers", when
+  enabled ([#6820]).
+
+  **NOTE:** Disabling private RDNS resolution behaves effectively the same as if
+  no private reverse DNS servers provided by user and by the OS.
+
 ### Fixed
 
 - Statistics for 7 days displayed by day on the dashboard graph ([#6712]).
@@ -41,6 +50,7 @@ NOTE: Add new changes BELOW THIS COMMENT.
 [#6711]: https://github.com/AdguardTeam/AdGuardHome/issues/6711
 [#6712]: https://github.com/AdguardTeam/AdGuardHome/issues/6712
 [#6740]: https://github.com/AdguardTeam/AdGuardHome/issues/6740
+[#6820]: https://github.com/AdguardTeam/AdGuardHome/issues/6820
 
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 NOTE: Add new changes ABOVE THIS COMMENT.