code: private function getOptionsAvailable($entity)
      {
          $options = $this->getParameter('chill_custom_fields.'
                . 'customizables_entities');
                  
          foreach($options as $key => $definition) {
              if ($definition['class'] == $entity) {
                  foreach ($definition['options'] as $key => $value) {
                      yield $key;
                  }
              }
          }
            //    [$entity->getEntity()];
      }
docs: Return an array of available key option for custom fields group
  on the given entity
  
  @param string $entity the entity to filter