User or username parameter?

### Describe the usage question you have. Please include as many useful details as possible.

The page https://arrow.apache.org/docs/java/flight_sql_jdbc_driver.html lists "user" as the param for providing a user ID. However the example URL on the page shows a "username" parameter being used. Which is correct?

### Component(s)

Other

從 issue 中指定的 Flight SQL JDBC driver 文件頁面開始，將參數 "user" 的描述與使用 "username" 的範例 URL 進行比較。確認 Java driver 接受哪個參數，然後更新文件，讓描述和範例一致地指出正確的參數。

由索引模型根據 Issue 內容生成。