Flight SQL Server sends incorrect response for DoPutUpdateResult

[avantgardnerio]

Describe the bug

The Flight SQL Server incorrectly does a as_any() and sends a protobuf enum instead of the message itself. This is incompatible with the JDBC implementation. (As usual, the spec itself is unclear). It results in the record_count being 0 instead of -1 which means a proper client implementation will poll forever.

To Reproduce

This one is a doozy to reproduce:

1. Run this fork of ballista
2. Build this fork of the JDBC driver
3. Install the fat jar driver into your favorite SQL tool
4. Run an update query, observe the tool hang as it follows the spec attempting to wait for the condition to be met:

There are no more results when the following is true:

     // stmt is a Statement object
     ((stmt.getMoreResults(current) == false) && (stmt.getUpdateCount() == -1))

Expected behavior

The query succeeds.

[avantgardnerio]

Tagging @tustvold and @andygrove , thank you both for your help!