title: Set billing_address_2 label in Woocommerce checkout
body: <p>I'm trying to set / show a label for the billing_address_2 field on the Woocommerce checkout page, but can't find a way to do this. Does anyone know a solution?</p>
  
  <p>The code below (which works fine on other fields) does not do the job.</p>
  
  <pre><code>add_filter( 'woocommerce_checkout_fields' , 'custom_rename_wc_checkout_fields' );
  
  function custom_rename_wc_checkout_fields( $fields ) {
  
      $fields['billing']['billing_address_2']['label'] = 'Building number';
      return $fields;
  
  }
  </code></pre>