Fix foreign key constraints

[benc-db]

Resolves #784

Description

Looking into #784, constraints strip off config that dbt hasn't specified, so parent and parent_columns were not making it to the macro. It looks as though 'to' and 'to_columns' can fill this role instead. Will need to update any documentation out there that references parent and parent_columns.

Checklist

• [x] I have run this code in development and it appears to resolve the stated issue
• [x] This PR includes tests, or tests are not required/relevant for this PR
• [x] I have updated the CHANGELOG.md and added information about my change to the "dbt-databricks next" section.

[eric-wang-1990]

Need a little more context to understand, seems we are only changing what we expect the users to provide for the foreign key table and column. You mention parent and parent_columns are not working because of dbt will strip it out? Does to and to_columns work because that's a supported keyword by dbt? Any documents reference?

[benc-db]

Need a little more context to understand, seems we are only changing what we expect the users to provide for the foreign key table and column. You mention parent and parent_columns are not working because of dbt will strip it out? Does to and to_columns work because that's a supported keyword by dbt? Any documents reference?

Exactly. And no, these columns are not referenced in the docs I can find, but are public fields on the ModelConstraint class.