[8.x] add schedule:clear-mutex command

[bernardwiesner]

Currently there is no way to clear the mutex files created when using withoutOverlap(). The only way to clear them is using php artisan cache:clear however this is dangerous since it clears all other cache as well.

If your server restarts while a task is running, the mutex file does not get deleted. Then when the server comes up, it could take up to 24 hours (default value) for your task to re-run because the mutex file still exists. The only way currently to solve this is just running cache:clear however this is not optimal.

In order to delete only mutex files I added a schedule:clear-mutex command.

[bernardwiesner]

Adding an option like:
schedule:clear-mutex {signature?} would also be useful. I can add that too if there is a willingness for this feature.

[bernardwiesner]

just FYI Taylor renamed the method to schedule:clear-cache