Pull request: scripts: add network-control plug

Updates #3976.

Squashed commit of the following:

commit 49d8a3a2d333c7896530c8a44c5ef06c396b5ae0
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Dec 22 16:20:45 2021 +0300

    scripts: add network-control plug

scripts/snap/snap.tmpl.yaml

@@ -29,6 +29,11 @@
     # (cap_net_bind_service) and also to bind to a particular interface using
     # SO_BINDTODEVICE (cap_net_raw).
     - 'network-observe'
+    # Add the "network-control" plug to be able to use raw sockets in the DHCP
+    # server.
+    #
+    # TODO(a.garipov): If this works, request auto-connect of this plug.
+    - 'network-control'
     'daemon': 'simple'
     'restart-condition': 'always'
   'adguard-home-web':