Add constants for Product MinMax Active

src/main/edu/wisc/services/cbs/product/Product.php

@@ -11,6 +11,13 @@ use Money\Money;
  */
 class Product
 {
+
+    /** @var string CBS value for MinMax active */
+    const MIN_MAX_ACTIVE = 'yes';
+
+    /** @var string CBS value for MinMax inactive */
+    const MIN_MAX_INACTIVE = 'no';
+
     /** @var float  Stock Keeping Unit, a unique product identifier */
     private $sku;