These flags are not commonly invoked by users, causing issues when cleaning up old containers. Rather than instruct users to use some random flag, just change the default to what is likely to be more common.
There was a missing placeholder in the template string.
That caused that `%!(EXTRA string=...` is added to the crontab file which causes commands to fail.
This allows alternative plugins - such as dokku-letsencrypt - to inject scheduled cron tasks into the cron system used by Dokku. Cron systems can choose to include or not include a cron task based on the specified scheduler, and can also optionally use a third parameter to store arbitrary information.
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.
