Improve YOJ error messages and transaction log messages #204
Description
Some of them, e.g., EntityAlreadyExistsException, are not very helpful because YDB doesn't provide information on which constraint was violated (and with what key column values). Also, YDB error messages include "request" and "response" which are, more often than not, near useless for diagnosing the problem.
There is a preliminary PR/branch for this Issue.
This Issue will be addressed after #165, because that new functionality already brings many changes to YOJ exceptions and handling thereof.