This occurs during the postdeploy on the first deploy of an app, mimicking heroku. It currently happens _after_ the `postdeploy` and `release` deploy tasks.
This functionality enables users to manage a global crontab for the Dokku user that contains all scheduled tasks across all apps. Alternative schedulers can implement cron tasks as desired.
Rather than waiting for the next deploy, take advantage of the retire system to retire these containers immediately.
Note that since the retire process happens out of band, the containers may stick around for up to 5 minutes, after which point they will be removed.
Customization of the wait time to retire - currently 60 seconds - is up for future debate. The containers ultimately haven't been useful for debugging, so keeping them around for longer won't help in most cases, and folks can disable the dokku-retire service (or cron) if that is desired.
Previous versions extracted the values as strings, prefixing the values with `/bin/sh -c '$CMD'` unnecessarily. This caused issues where we would incorrectly overrride these values when an app had a predeploy script.
Closes#3143
