Allow setting transport connection persistency

Author: damijank

src/DependencyInjection/Configuration.php

@@ -488,6 +488,7 @@ private function addClientsSection(ArrayNodeDefinition $rootNode)
                                         ->scalarNode('retryOnConflict')
                                             ->defaultValue(0)
                                         ->end()
+                                        ->booleanNode('persistent')->defaultValue(true)->end()
                                     ->end()
                                 ->end()
                             ->end()