[Java][FlightRPC] Update benchmark to be on par with C++

See https://github.com/apache/arrow/issues/13980

The Java benchmark isn't comparable out of the box (and it seems like there's an unexplained gap between it and the C++ benchmark)

**Reporter**: [David Li](https://issues.apache.org/jira/browse/ARROW-17537) / @lidavidm

_{**Note**: *This issue was originally created as [ARROW-17537](https://issues.apache.org/jira/browse/ARROW-17537). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Start by reading the linked Apache Arrow issue 13980 and compare the Java FlightRPC benchmark with its C++ counterpart. Identify why the benchmarks are not comparable and what causes the reported performance gap. Done means the Java benchmark is aligned with the C++ benchmark and produces comparable results.

Written by the indexing model from the issue text.