arrow

GH-36476: [C++][FlightRPC] Fix uninitialized fields in FlightInfo (#36484)



### Rationale for this change

Fix CI

### What changes are included in this PR?

Provide initializers for fields

### Are these changes tested?

It's UB so it's hard to have a deterministic test

### Are there any user-facing changes?

No
* Closes: #36476

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>