Add .env var for api_version

Author: ryanmitchell

config/shopify.php

@@ -56,7 +56,7 @@
     /**
      * Admin API version - Set this to a fixed value (eg 2023-07) or null to let the library decide
      */
-    'api_version' => null,
+    'api_version' => env('SHOPIFY_API_VERSION', null),
 
     /**
      * Admin connection is a private app, defaults to false