HHH-7357 - Constraint violation exception while inserting NULL to not nullable column

Patch and test for HHH-7357 JIRA ticket.
Link: https://hibernate.atlassian.net/browse/HHH-7357

In my opinion dialect specific exception recognition could be moved from SQLStateConversionDelegate#convert(SQLException, String, String) to Dialect#buildSQLExceptionConversionDelegate(). See detection of MySQL and Oracle query interruption, and Derby lock obtaining timeout - https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/exception/internal/SQLStateConversionDelegate.java#L142.

Regards,
Lukasz Antoniak