feat: add flysystem key (#705)

* feat: add flysystem key

* docs: add link for reference

Author: dsdeboer

rules/CodeQuality/Rector/Closure/StringExtensionToConfigBuilderRector.php

@@ -51,6 +51,8 @@ final class StringExtensionToConfigBuilderRector extends AbstractRector
         'maker' => 'Symfony\Config\MakerConfig',
         'nelmio_cors' => 'Symfony\Config\NelmioCorsConfig',
         'api_platform' => 'Symfony\Config\ApiPlatformConfig',
+        // @see https://github.com/thephpleague/flysystem-bundle/blob/3.x/src/DependencyInjection/Configuration.php
+        'flysystem' => 'Symfony\Config\FlysystemConfig',
     ];
 
     public function __construct(