[DOCS]: Better docs for foreign key declaration

### Describe what you want

In the [documentation for defining a foreign key constraint](https://orm.drizzle.team/docs/indexes-constraints#foreign-key), it shows how to specify a name, source columns and foreign columns but doesn't show to to specify the `on update` and `on delete` actions. Might be worth adding as especially when declaring a composite foreign key, it's not obvious how to do this.