launchd: make Launch Agents config a freeform setting

Because there probably are options we don't know about.

modules/launchd/launchd.nix

@@ -28,6 +28,8 @@
 with lib;
 
 {
+  freeformType = with types; attrsOf anything; # added by Home Manager
+
   options = {
     Label = mkOption {
       type = types.str;

tests/modules/launchd/agents.nix

@@ -13,6 +13,7 @@ with lib;
           SuccessfulExit = false;
         };
         ProcessType = "Background";
+        UnrecognizedByHomeManager = "should make it to the resulting plist";
       };
     };
 

tests/modules/launchd/expected-agent.plist

@@ -19,5 +19,7 @@
 		<string>--with-arguments</string>
 		<string>foo</string>
 	</array>
+	<key>UnrecognizedByHomeManager</key>
+	<string>should make it to the resulting plist</string>
 </dict>
 </plist>