[6.x] Support job middleware for queued notifications

[vigneshgurusamy]

Implementation for issue #30057

[taylorotwell]

I wouldn't have a property at all. Just check the method.

[vigneshgurusamy]

@taylorotwell Both Job and Notification classes use Queuable trait which implements through() method to set middlewares.

If we remove the property check, we will lose the ability to set middleware via through() method.

Still, users will be able to call through() method from queued notification but middlewares won't be added to queued notification job from the property.

So how do we solve this?