Pull request: 3955-doh3

Updates #3955.

Squashed commit of the following:

commit acfd5ccc29ff03dfae1e51e52649acdf05042d9f
Merge: caeac6e5 61bd217e
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Oct 3 18:00:37 2022 +0300

    Merge branch 'master' into 3955-doh3

commit caeac6e5401bcaa95bba8d2b84a943b6c9a5898a
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Oct 3 17:54:16 2022 +0300

    all: fix server closing; imp docs

commit 87396141ff49d48ae54b4184559070e7885bccc7
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Oct 3 17:33:39 2022 +0300

    all: add doh3 support

CHANGELOG.md

@@ -22,12 +22,28 @@ and this project adheres to
   /control/stats_reset` requests) do not have a `Content-Type` header set on
   them ([#4970]).
 
+### Added
+
+#### Experimental HTTP/3 Support
+
+See [#3955] and the related issues for more details.  These features are still
+experimental and may break or change in the future.
+
+- DNS-over-HTTP/3 DNS and web UI client request support.  This feature must be
+  explicitly enabled by setting the new property `dns.serve_http3` in the
+  configuration file to `true`.
+- DNS-over-HTTP upstreams can now upgrade to HTTP/3 if the new configuration
+  file property `use_http3_upstreams` is set to `true`.
+- Upstreams with forced DNS-over-HTTP/3 and no fallback to prior HTTP versions
+  using the `h3://` scheme.
+
 ### Fixed
 
 - User-specific blocked services not applying correctly ([#4945], [#4982],
   [#4983]).
 - `only application/json is allowed` errors in various APIs ([#4970]).
 
+[#3955]: https://github.com/AdguardTeam/AdGuardHome/issues/3955
 [#4970]: https://github.com/AdguardTeam/AdGuardHome/issues/4970