Custom job status model

[vpratfr]

Would be nice to be able to use our own job status model class when we need to add some features to it.

This should not be hard :

• add a config file to provide the fully qualified class name
• make migration publishable (#16)
• use the config class to get the table name in the migration
• use the config class here and there when we need to create the model

You have a good example of how to provide such configurable model feature in spatie/laravel-model-status package