feat: Add relations to destination tests

[candiduslynx]

Are you positive this feature should be implemented in the SDK?

• I'm positive this is an SDK feature

Which problem is this feature request solving?

Forgetting to flatten tables or traverse the relations during migration

Describe the solution you'd like

Add the relation table to the destination test to verify that the destination migrates as expected and is able to write to a child table

Pull request (optional)

• I can submit a pull request