[8.x] Adds Model key extraction to id on whereKey() and whereKeyNot()

[DarkGhostHunter]

This PR allows to get the key of a Model when a Model instance is issued on whereKey() and whereKeyNot() methods to the Builder for relationships.

Problem & Solution

If a developer issues a Model instance to whereKey() or whereKeyNot(), these methods will make a WHERE IN clause with all the model attributes, mainly because a Model implements Arrayable.

To avoid this, these methods will check first if the $id is a Model instance, and get the key from it.

$passenger->tickets()->whereHas('airline', fn (Builder $query) => $query->whereKey($airline))->get();

[netpok]

I like this feature, but in my opinion it should support multiple keys too.

$forExample->whereKey([$model1, $model2])->get();