code: public function process(ContainerBuilder $container)
      {
          $imageScaler = $container->getDefinition('dothiv_contentful.image_asset_scaler');
          foreach ($container->getParameter('dothiv_contentful.thumbnails') as $label => $thumbnailConfig) {
              $imageScaler->addMethodCall(
                  'addSize',
                  array(
                      $label,
                      $thumbnailConfig['width'],
                      $thumbnailConfig['height'],
                      $thumbnailConfig['thumbnail'],
                      $thumbnailConfig['exact'],
                      $thumbnailConfig['fillbg']
                  )
              );
          }
      }
docs: {@inheritdoc}