Add support for related instance table alias

[toitzi]

This PR aims to add support for also aliasing the related instance. This change is non breaking.

e.g:

class Comment extends Model
{
    use \Znck\Eloquent\Traits\BelongsToThrough;

    public function grandparent(): \Znck\Eloquent\Relations\BelongsToThrough
    {
        return $this->belongsToThrough(
            Comment::class . ' as relation', // -> THIS IS NEW
            Comment::class . ' as alias',
            foreignKeyLookup: [Comment::class => 'parent_id']
        );
    }
}

The reason for this is i have a belongsToThrough relation, which ends up at the model itself.
E.g. (Not really posts in my case just an example):

1. A posts table
2. A posts_relation table (which has a column "parent_post_id" and "post_id")

And now I have a post where i want to get it's parent post which is easy to archive thanks to this library, however when using it not only on a single post but on a collection, for example with "whereDoesNotHave" e.g "Posts::whereDoesNotHave('parentPost')", the query will not work, since the table names collide. Therefore aliasing on a releated table is needed.

[staudenmeir]

Hi @toitzi,
Thanks, I'll take a look.