PW-1518: add 24x installments options

Block/Adminhtml/System/Config/Field/Installment.php

@@ -41,7 +41,19 @@ class Installment extends \Magento\Framework\View\Element\Html\Select
                             '9' => '9x',
                             '10' => '10x',
                             '11' => '11x',
-                            '12' => '12x'
+                            '12' => '12x',
+                            '13' => '13x',
+                            '14' => '14x',
+                            '15' => '15x',
+                            '16' => '16x',
+                            '17' => '17x',
+                            '18' => '18x',
+                            '19' => '19x',
+                            '20' => '20x',
+                            '21' => '21x',
+                            '22' => '22x',
+                            '23' => '23x',
+                            '24' => '24x'
     ];
 
     /**