Add Unwrap methods for bolt errors

[arxeiss]

Error types are in internal package, so casting is not possible. And because of missing Unwrap method, the errors.Is() doesn't work either.

Closing #631

[arxeiss]

Is there anything I can do to make this PR to be merged?

[StephenCathcart]

Hi @arxeiss,

Thank you for taking the time to contribute. We appreciate all community engagement.
Before we review a change, we require that users have signed our Contributor License Agreement(CLA). This allows the "whitelist-check (pull-request)" part of our build process to pass.
For more details on signing our CLA, please see: https://neo4j.com/developer/cla/. Specifically, the 'How to Sign' section.

I've also updated this PR to point towards our 6.x branch, as 5.28 is now Long-Term Support (LTS).

[StephenCathcart]

Hey @arxeiss, thanks for signing our CLA. The change looks very reasonable. We're currently in the process of updating our pipelines for our upcoming 6.0 release, so I'll be sure to include this PR with that. Thanks again for the contribution 👍.