Pull request: 4216 simpl hosts

Merge in DNS/adguard-home from 4216-hosts-explode to master

Updates #4216.

Squashed commit of the following:

commit a6ed131923496d9bbd1d80c652d4584951528c4a
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 27 19:11:23 2022 +0300

    aghnet: imp docs

commit 25cca065c3c6dc227288cdd0803dc3ff8f9c3ca4
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 27 18:53:16 2022 +0300

    aghnet: simpl hosts container

CHANGELOG.md

@@ -56,6 +56,11 @@ In this release, the schema version has changed from 12 to 13.
 -->
 - Go 1.17 support.  v0.109.0 will require at least Go 1.18 to build.
 
+## Fixed
+
+- Unnecessarily complex hosts-related logic leading to infinite recursion in
+  some cases ([#4216]).
+
 ### Removed
 
 - Go 1.16 support.