erp5_hal_json_style: export DateTime in gadget field extra parameter

bt5/erp5_hal_json_style/SkinTemplateItem/portal_skins/erp5_hal_json_style/ERP5Document_getHateoas.py

@@ -702,7 +702,7 @@ def renderField(traversed_document, field, form, value=MARKER, meta_type=None,
       "sandbox": field.get_value("js_sandbox")
     })
     try:
-      result["renderjs_extra"] = json.dumps(dict(field.get_value("renderjs_extra")))
+      result["renderjs_extra"] = json.dumps(toBasicTypes(dict(field.get_value("renderjs_extra"))))
     except KeyError:
       # Ensure compatibility if the products are not yet up to date
       result["renderjs_extra"] = json.dumps({})