It would be great to be able to trigger a specific cron command like so:

dokku cron:run $APP $CRON_ID

If no $CRON_ID is specified, then we can interactively ask for the desired cron id after listing the existing cron tasks for the given app.

This would trigger a scheduler-cron-trigger $SCHEDULER $APP $CRON_ID $COMMAND_ARGS call, which would then do the right thing for the scheduler in use.