export: add logger to make feedback on deployed instances easier to debug

src/Bundle/ChillMainBundle/Controller/ExportController.php

@@ -442,6 +442,12 @@ class ExportController extends AbstractController
         }
 
         $rawData = unserialize($serialized);
+
+        $this->logger->notice('[export] choices for an export unserialized', [
+            'key' => $key,
+            'rawData' => json_encode($rawData)
+        ]);
+
         $alias = $rawData['alias'];
 
         $formCenters = $this->createCreateFormExport($alias, 'generate_centers');