Pull request: 1947 flag for /etc/hosts

Merge in DNS/adguard-home-wiki from 1947-opt-hosts to master

Squashed commit of the following:

commit 4307ab657c8a24259af23a69804e31116d7164f0
Merge: 4751c87 5e1918f
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Apr 12 18:35:11 2021 +0300

    Merge branch 'master' into 1947-opt-hosts

commit 4751c87cc32015ad8d9e11659fcbae58672bea0d
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Apr 12 17:50:48 2021 +0300

    Configuration: --no-etc-hosts flag

Configuration.md

@@ -34,6 +34,7 @@ Options:
   --check-config                     Check configuration and exit
   --no-check-update                  Don't check for updates
   --no-mem-optimization              Disable memory optimization
+  --no-etc-hosts                     Do not use the OS-provided hosts.
   -v, --verbose                      Enable verbose output
   --glinet                           Run in GL-Inet compatibility mode
   --version                          Show the version and exit. Show more detailed version description with -v