nixos/unbound: deprecate extraConfig in favor of settings

Follow RFC 42 by having a settings option that is
then converted into an unbound configuration file
instead of having an extraConfig option.

Existing options have been renamed or kept if
possible.

An enableRemoteAccess has been added. It sets remote-control setting to
true in unbound.conf which in turn enables the new wrapping of
unbound-control to access the server locally.  Also includes options
'remoteAccessInterfaces' and 'remoteAccessPort' for remote access.

Signed-off-by: Marc 'risson' Schmitt <marc.schmitt@risson.space>

nixos/doc/manual/release-notes/rl-2105.xml

@@ -829,6 +829,23 @@ environment.systemPackages = [
      default in the CLI tooling which in turn enables us to use
      <literal>unbound-control</literal> without passing a custom configuration location.
     </para>
+
+    <para>
+     The module has also been reworked to be <link
+     xlink:href="https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md">RFC
+     0042</link> compliant. As such,
+     <option>sevices.unbound.extraConfig</option> has been removed and replaced
+     by <xref linkend="opt-services.unbound.settings"/>. <option>services.unbound.interfaces</option>
+     has been renamed to <option>services.unbound.settings.server.interface</option>.
+    </para>
+
+    <para>
+     <option>services.unbound.forwardAddresses</option> and
+     <option>services.unbound.allowedAccess</option> have also been changed to
+     use the new settings interface. You can follow the instructions when
+     executing <literal>nixos-rebuild</literal> to upgrade your configuration to
+     use the new interface.
+    </para>
    </listitem>
    <listitem>
     <para>