Merge in DNS/dnsproxy from imp-xff to master

Updates AdguardTeam/AdGuardHome#2799.

Squashed commit of the following:

commit aef68d4448724c6f5f89f069e2503f2b414dbe91
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Jul 23 16:30:09 2021 +0300

    proxy: trim spaces

commit bf36249e1e47a33bb712067be9966f4d3c6afdf0
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Jul 23 16:11:36 2021 +0300

    proxy: fix logic

commit f381fe208cbc3b4783a14d3ffde6885c242a9dcc
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Jul 22 19:56:25 2021 +0300

    all: upd go version to 1.16 in specs

commit 54b9fbd10ac68b81ce9a03391b13872e859ff86e
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Jul 22 19:52:59 2021 +0300

    all: upd go version to 1.16 for github

commit a2cd74d0b79a2f4ddd7ec46dff18746041ad4028
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Jul 22 19:47:10 2021 +0300

    proxy: imp code

commit a8ae14ff9543732b6bdc1a8ac7479b6007b65018
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Jul 22 16:35:03 2021 +0300

    proxy: add trusted proxies