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

从 issue 中指定的 Flight SQL JDBC driver 文档页面开始，将参数 "user" 的描述与使用 "username" 的示例 URL 进行比较。验证 Java driver 接受哪个参数，然后更新文档，使描述和示例一致地标识正确的参数。

由索引模型根据 Issue 内容生成。