Pull request: 3142 custom private subnets

Merge in DNS/adguard-home from 3142-custom-subnets to master

Updates #3142.

Squashed commit of the following:

commit 11469ade75b9dc32ee6d93e3aa35cf79dbaa28b2
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Mar 17 19:56:02 2022 +0300

    all: upd golibs, use subnet set

CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to
 
 ### Added
 
+- The ability to customize the set of networks considered private through the
+  new `private_networks` setting ([#3142]).
 - EDNS Client-Subnet information in the request details section of a query log
   record ([#3978]).
 - Support for hostnames for plain UDP upstream servers using the `udp://` scheme
@@ -88,6 +90,7 @@ In this release, the schema version has changed from 12 to 13.
 [#1730]: https://github.com/AdguardTeam/AdGuardHome/issues/1730
 [#2993]: https://github.com/AdguardTeam/AdGuardHome/issues/2993
 [#3057]: https://github.com/AdguardTeam/AdGuardHome/issues/3057
+[#3142]: https://github.com/AdguardTeam/AdGuardHome/issues/3142
 [#3367]: https://github.com/AdguardTeam/AdGuardHome/issues/3367
 [#3381]: https://github.com/AdguardTeam/AdGuardHome/issues/3381
 [#3503]: https://github.com/AdguardTeam/AdGuardHome/issues/3503