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GH-38460: [Java][FlightRPC] Add mTLS support for Flight SQL JDBC driver (#38461)



### Rationale for this change

I wanted to add additional security capabilities to the Arrow Flight SQL JDBC driver so that it catches up to ADBC.  ADBC already supports mTLS - and it is a great security feature.  I wanted to bring this to the JDBC driver as well.

### What changes are included in this PR?

This PR adds support for mTLS (client certificate verification/authentication) to the Arrow Flight SQL JDBC driver.

### Are these changes tested?

Yes, I've added tests of the new mTLS functionality - and have ensured that the change is backward compatible by verifying all existing tests pass.

### Are there any user-facing changes?

Yes - but the end-user documentation for the Arrow Flight SQL JDBC driver has been updated in the PR itself.

* Closes: #38460

Lead-authored-by: prmoore77 <prmoore77@hotmail.com>
Co-authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>