ftpwriter连接及写出数据格式支持确认

（1）ftpwriter是否支持私钥文件作为密码连接SFTP服务器？
（2）ftpwriter 文件写出的格式是否支持parquet格式？

The issue only asks whether ftpwriter supports private-key SFTP authentication and Parquet output; no file or test is named. First inspect the ftpwriter documentation and implementation, then verify both capabilities against the existing configuration and tests. Done should be a documented answer, or a narrowly scoped feature request if either capability is unsupported.

Written by the indexing model from the issue text.