Add validation of JPA Entities against real db schema

[mfvanek]

Hibernate can do such validation on startup but usually in real apps it isn't an appropriate behavior.

• https://stackoverflow.com/questions/47839163/how-can-i-validate-the-database-schema-against-my-jpa-in-wildfly-11-hibernate
• https://stackoverflow.com/questions/54464978/validate-schema-programmatically-using-hibernate
• https://stackoverflow.com/questions/2327423/how-to-validate-database-schema-programmatically-in-hibernate-with-annotations