title: Add custom fields to nav-menu item
body: <p>I am trying to add custom data to my menu items (say, for example, <code>data-*</code> attributes) or a dropdown to select the link <code>target</code>, etc. </p>
  
  <p>Through the Screen Options, we have Link Target, Title Attribute, CSS Classes, Link Relationship (XFN) and Description (see screenshot below), but none really offer what I want.</p>
  
  <p><a href="https://i.stack.imgur.com/KoS1S.png" rel="nofollow"><img src="https://i.stack.imgur.com/KoS1S.png" alt="Default menu item fields"></a></p>
  
  <p>I thought of looking for extensions to Advanced Custom Fields, or something of the sort, but I have not seen anything like it, nor anything through my theme functions.php file. </p>