Added action before the rendering of a zone's methods

* The new action will allow to add elements to the page without having to override the view.

includes/admin/settings/views/html-admin-page-shipping-zone-methods.php

@@ -10,6 +10,8 @@ if ( ! defined( 'ABSPATH' ) ) {
 	<?php echo wc_help_tip( __( 'The following shipping methods apply to customers with shipping addresses within this zone.', 'woocommerce' ) ); ?>
 </h2>
 
+<?php do_action('wc_shipping_zone_before_methods_list'); ?>
+
 <table class="wc-shipping-zone-methods widefat">
 	<thead>
 		<tr>