Use morph-name instead of class-name for a tag

[Cellard]

If job has no explicit tags, Horizon builds tags with every model, passed to a job constructor. Model's tag is a full class name and primary key.

I think, that we may use model's morph name intead of class name. It would be more laconic.

You can see the difference:

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If possible, please consider releasing your code as a package so that the community can still take advantage of your contributions!

If you feel absolutely certain that this code corrects a bug in the framework, please "@" mention me in a follow-up comment with further explanation so that GitHub will send me a notification of your response.