DB2 by default does NOT enable foreign key constraints

[victorterpstra]

DB2 by default does not enable ('enforce') foreign key checks.
Tables will be created with the NOT ENFORCED option.

According to https://www.ibm.com/docs/en/db2/10.5?topic=constraints-creating-modifying, after the table has been created it needs to be modified using an 'ALTER TABLE` SQL operation.

In order to do the ALTER, we need the name of the constraint.
That requires either:

• Explicitly specify a unique name in a ForeignKey constraint, or
• Enable automated naming sqlalchemy.MetaData(schema=schema, naming_convention=CONVENTION)

See also:

• https://docs.sqlalchemy.org/en/14/core/constraints.html
• https://docs.sqlalchemy.org/en/14/core/constraints.html#creating-dropping-foreign-key-constraints-via-alter
• https://www.ibm.com/docs/en/db2/10.5?topic=constraints-creating-modifying
• https://stackoverflow.com/questions/54513136/when-we-should-use-not-enforced-with-foreign-key-constraint-in-db2