title: Set custom product sorting as default Woocommerce sorting option
body: <p>In Woocommerce, I ma using the following code that adds a custom sorting option to shop catalog by modified date.</p>
  
  <pre><code>add_filter( 'woocommerce_get_catalog_ordering_args', 'enable_catalog_ordering_by_modified_date' );
  function enable_catalog_ordering_by_modified_date( $args ) {
      if ( isset( $_GET['orderby'] ) ) {
          if ( 'modified_date' == $_GET['orderby'] ) {
              return array(
                  'orderby'  =&gt; 'modified',
                  'order'    =&gt; 'DESC',
              );
          }
      }
      return $args;
  }
  
  add_filter( 'woocommerce_catalog_orderby', 'add_catalog_orderby_by_modified_date' );
  function add_catalog_orderby_by_modified_date( $orderby_options ) {
      // Rename 'menu_order' label
      $orderby_options['modified_date'] = __("Sort by modified date", "woocommerce");
  
      return $orderby_options ;
  }
  </code></pre>
  
  <p>From this answer: <a href="https://stackoverflow.com/questions/53573475/add-sorting-by-modified-date-in-woocommerce-products-sort-by">Add sorting by modified date in Woocommerce products sort by</a></p>
  
  <p>I would like to make that custom sorting option as the default sorting option keeping the default woocommerce option (by menu order) as a secondary option.</p>
  
  <p>How can I set this sorting as woocommerce default?</p>