Updates AdguardTeam/AdGuardHome#6882.

Squashed commit of the following:

commit 7b1e4fad6db9204d1cc9accb133163f98509c9ce
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Apr 18 15:38:06 2024 +0300

    all: imp docs

commit 5a19fc5c
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Apr 17 17:16:12 2024 +0300

    README: imp docs

commit 42cc70cd
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Apr 17 16:33:00 2024 +0300

    all: imp docs

commit 1862caa7
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Apr 16 19:55:24 2024 +0300

    proxy: use private upstreams for ns & soa