[Java][FlightSQL] Arrow Flight SQL JDBC Driver returns -1 for getUpdateCount()

### Describe the bug, including details regarding any error messages, version, and platform.

Tested on Arrow Flight JDBC 15, 15.02 and with a locally-built Arrow Flight SQL JDBC Driver 17.0.0-SNAPSHOT.

When using a JDBC statement to execute an UPDATE, the getUpdateCount() method seems to always return -1. This seems to be incorrect. The getUpdateCount() should return the number of rows UPDATEd.

For a data source, we're using the [Voltron docker container](https://hub.docker.com/r/voltrondata/flight-sql)

In this debugger image, you can see the return counts from the getUpdateCount() and from the actual result set (the update returns one row, with one column, that indicates the number of UPDATEd rows.

Here is a screen grab of the output data:

And, in this screengrab, I used the Postgres driver to update a table in postgres:latest Docker image:

The data in the Postgres table is different, but the getUpdateCount() method returned 1 which is correct for that data.
The test program I used is checked into this Github repo: [ZD128958](https://github.com/rcprcp/ZD128958)

Thank you!

### Component(s)

Java

Beginne damit, das Testprogramm ZD128958 gegen den Arrow Flight SQL JDBC Driver auszuführen, und vergleiche Statement.getUpdateCount() mit dem zurückgegebenen Resultset für ein UPDATE. Verfolge den Pfad im JDBC-Treiber, der UPDATE-Ergebnisse verarbeitet; abgeschlossen ist die Aufgabe, wenn getUpdateCount() die Anzahl der aktualisierten Zeilen meldet, wie es der PostgreSQL-Treiber tut.

Vom Indexierungsmodell aus dem Issue-Text verfasst.