ENGCOM-3335: Added $connection property to class #141

 - Merge Pull Request magento-engcom/import-export-improvements#141 from maxalmonte14/import-export-improvements:improvement/supress_undefined_connection_property_error
 - Merged commits:
   1. ac90f7a
   2. 6789eb4
   3. 7f3808c
   4. 5ff88c0

Author: magento-engcom-team

app/code/Magento/DownloadableImportExport/Helper/Uploader.php

@@ -38,6 +38,11 @@ class Uploader extends \Magento\Framework\App\Helper\AbstractHelper
      */
     protected $parameters = [];
 
+    /**
+     * @var \Magento\Framework\DB\Adapter\AdapterInterface
+     */
+    public $connection;
+
     /**
      * Construct
      *