filter added in dev-doc

Author: julitafalcondusza

docs/templating/twig_function_reference/product_twig_functions.md

@@ -129,4 +129,15 @@ The `ibexa_is_pim_local` is a helper Twig function that enables changing the beh
         <button type="button">Modify product data</button>
     </div>
 {% endif %}
+```
+
+### `ibexa_product_catalog_group_attributes`
+
+The `ibexa_product_catalog_group_attributes` filter groups product attributes (configured in `ibexa_product_catalog_group_attributes`).
+
+#### Example
+
+``` html+twig
+{% for group, attributes in product.attributes | ibexa_product_catalog_group_attributes %}
+{{ group.getIdentifier() }}:{{ attributes|map(attribute => attribute.getAttributeDefinition().getIdentifier())|join(' ') }}
 ```