pulseaudio module: add extraClientConf option

nixos/modules/config/pulseaudio.nix

@@ -27,6 +27,7 @@ let
   clientConf = writeText "client.conf" ''
     autospawn=${if nonSystemWide then "yes" else "no"}
     ${optionalString nonSystemWide "daemon-binary=${cfg.package.out}/bin/pulseaudio"}
+    ${cfg.extraClientConf}
   '';
 
   # Write an /etc/asound.conf that causes all ALSA applications to
@@ -96,6 +97,14 @@ in {
         '';
       };
 
+      extraClientConf = mkOption {
+        type = types.str;
+        default = "";
+        description = ''
+          Extra configuration appended to pulse/client.conf file.
+        '';
+      };
+
       package = mkOption {
         type = types.package;
         default = pulseaudioLight;