[12.x] Add enum support for job method in scheduler

[amirhshokri]

This PR adds enum support for the $queue and $connection parameters in $schedule->job() method:

$schedule->job(TestJob::class, QueueType::DEFAULT, ConnectionType::REDIS);

[taylorotwell]

I think I would prefer to have one unified PR to add Enum support to every single documented place in the framework it makes sense to use them vs. continuing to add support in one place at a time.

[amirhshokri]

Thanks for reviewing the PR @taylorotwell
Do you mean these changes should be applied throughout the entire project, or just in the queue-related parts?
Because in the first case, the amount of changes would be quite large.

[shaedrich]

If that was to happen, it would probably make sense to create a branch here directly and divide the work between different people 🤔