add relationships on same table examples

[faeby]

As requested in rappasoft/laravel-livewire-tables#1190, this is an attempt to add examples for relationships on the same table.

These examples are interesting because they show the behavior for:

• a relationship that is on the same table that the original queried model
• a relationship of the first relation on the same table

So we have a base table and 2 relationships from the same origin.

This PR is a draft because it will generate an SQL until the PR in the package repository is merged.