Further improvements

- Add callback for when a select2 form field is updated
- Adjust selected quantity based on returned data
- auto_fill the stock_item field

InvenTree/templates/js/translated/forms.js

@@ -1426,6 +1426,11 @@ function initializeRelatedField(field, fields, options) {
                 data = item.element.instance;
             }
 
+            // Run optional callback function
+            if (field.onSelect && data) {
+                field.onSelect(data, field, options);
+            }
+
             if (!data.pk) {
                 return field.placeholder || '';
             }