Improve exceptions to support identifying more specific exceptions such as "constraint violation" and "duplicate key"

Currently there seems to be no easy way to check a PersistenceException to see if is a "Constraint violation" exception etc.

It would be good to have a provider agnostic and database agnostic way to as least easily identify "Constraint violation" exceptions and ideally a more specific "Unique constraint violation".

One possible approach would be to extend the exception hierarchy.

Start by reviewing PersistenceException and the existing exception hierarchy. Define how provider-agnostic and database-agnostic identification should work for constraint violations, including the proposed unique-constraint case. Done means the issue's requirements are resolved through an agreed exception design.

Written by the indexing model from the issue text.