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

Start with the Flight SQL JDBC driver documentation page named in the issue and compare its "user" parameter description with the example URL using "username". Verify which parameter the Java driver accepts, then update the documentation so the description and example consistently identify the correct parameter.

Written by the indexing model from the issue text.