Merge in GO/dnsproxy from AGDNS-1528-fallback-ups-conf to master

Squashed commit of the following:

commit d00ca113b07d4e489855cefa8ed110a382c7daf5
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Jun 30 14:33:53 2023 +0300

    all: imp code, docs

commit d9703445fd9e73cd466d603ff6543a5450330ffc
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Jun 30 13:15:36 2023 +0300

    proxy: close ups configs

commit ad2e2da0
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jun 29 16:03:16 2023 +0300

    proxy: imp fmt

commit 92918afb
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jun 29 15:58:51 2023 +0300

    proxy: imp code

commit 0dc3f3f3
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 28 20:35:54 2023 +0300

    proxy: imp code

commit a83136b7
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 28 18:47:30 2023 +0300

    proxy: fix name, typo

commit 08514218
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 28 18:46:11 2023 +0300

    proxy: fix lint

commit 2b282843
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 28 18:45:06 2023 +0300

    proxy: imp test, doc

commit 7487b537
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 28 18:26:20 2023 +0300

    proxy: imp docs

commit 146cbb95
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 28 18:21:12 2023 +0300

    proxy: imp tests

commit 3720aa42
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 28 14:16:35 2023 +0300

    all: imp code

commit 5c9ab059
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jun 22 17:53:00 2023 +0300

    all: make fallback an ups conf