manatee: Add ability to specify public url for homepage card

hosts/manatee/modules/homepage/default.nix

@@ -9,8 +9,13 @@ let
   nginxEnabled = config.mod.nginx.enable;
   services = config.mod.homepage.services;
 
-  serviceToCard = svc: ''
+  serviceToCard =
-    <a class="card" href="http://manatee:${toString svc.port}">
+    svc:
+    let
+      href = if svc.url != null then svc.url else "http://manatee:${toString svc.port}";
+    in
+    ''
+      <a class="card" href="${href}">
         <div class="name">${svc.name}</div>
         <div class="desc">${svc.description}</div>
         <div class="port">:${toString svc.port}</div>
@@ -83,6 +88,11 @@ in
               name = lib.mkOption { type = lib.types.str; };
               port = lib.mkOption { type = lib.types.port; };
               description = lib.mkOption { type = lib.types.str; };
+              url = lib.mkOption {
+                type = lib.types.nullOr lib.types.str;
+                default = null;
+                description = "Link target for the card; defaults to http://manatee:<port>.";
+              };
             };
           }
         );