Update arrow-flight with is_update field

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
- Related to https://github.com/apache/arrow/issues/49497

see vote https://lists.apache.org/thread/vpvqppjpv51gfcd7pqvozg3h7d5hnooh

It looks likely that the arrow-flight spec will add a new "is_update" field for ActionCreatePreparedStatementResult

We should update arrow-rs with this update too

**Describe the solution you'd like**
1. Update the FlightSQL protobuf definitions
2. Regenerate the rust structures
3. Add tests

**Describe alternatives you've considered**

**Additional context**

Start by checking the FlightSQL protobuf definitions and the existing regeneration workflow for Rust structures. Confirm the proposed is_update field against the linked Arrow specification discussion, then add coverage for ActionCreatePreparedStatementResult. Done means the definitions, generated Rust structures, and tests consistently include the field.

Written by the indexing model from the issue text.