feat request: Allow TablePartial to have composite foreign keys

I am hoping to do something like

```
Table relationship {
customer_id bigint
employee_id bigint
}

TablePartial rel {
customer_id bigint
employee_id bigint
}

Ref: rel(customer_id, employee_id) > relationship(customer_id, employee_id)

Table preferred_relationship {
~rel
category text
}
```
where each table that references a TablePartial will also create the same composite foreign key.

Do you think it is a good idea to add a feature like this? Thank you