[Java][FlightSQL] Implement transactions

[asfimport]

Acceptance Criteria

• TODO

Reporter: Tiffany Lam / @tifflhl

_{Note: This issue was originally created as ARROW-12932. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
I thought transactions weren't in the initial spec?

[asfimport]

Kyle Porter / @kylepbit:
Just looking through this, and you're correct, there's no transactions in the initial spec.

[lidavidm]

Transactions are supported.