Set cursor to "pointer" on .add-field hover

Currently, hovering the "Add field" button in the profile settings does not hint at it being clickable. The current behavior is inconsistent with the visibility scope buttons, which present the same visual design as the plus button on the add field option, yet do have pointer: cursor set. This MR changes the hover behavior so it becomes more intuitive and coherent.

src/components/settings_modal/tabs/profile_tab.scss

@@ -123,4 +123,8 @@
       margin: 0 .2em .5em;
     }
   }
+
+  .add-field {
+    cursor: pointer;
+  }
 }