feature: Allow unencrypted DOH

[krombel]

This is a first step to implement #1009.
This adds the config option

tls:
  allow_clear_doh: true

If allow_clear_doh is true (defaults to false), AdGuardHome allows serving DoH queries from bind_host:bind_port - so the normal http interface of AdGuardHome.

• Note
  If you want to pass the remote ip to AdGuardHome, you can setup nginx as follows:

        location /dns-query {
              proxy_set_header Host $http_host;
              proxy_set_header X-Real-IP $remote_addr;
              proxy_redirect off;
              proxy_buffering off;
              proxy_pass http://127.0.0.1:3000;
        }

[codecov-io]

Codecov Report

Merging #1276 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #1276   +/-   ##
=======================================
  Coverage   35.94%   35.94%           
=======================================
  Files          44       44           
  Lines        6805     6805           
=======================================
  Hits         2446     2446           
  Misses       4000     4000           
  Partials      359      359

Impacted Files	Coverage Δ
home/config.go	49.12% <ø> (ø)	⬆️
home/control.go	14.43% <0%> (ø)	⬆️

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