Cleanup old tasks and schedules #1125
Description
On zimit.kiwix.org instance, we want to automatically cleanup old tasks, requested tasks and schedules since these objects are not expected to be of any value once the task completes (the schedules are even supposed to be automatically cleaned up by the external system creating it ... but it does not always achieves to do so).
Zimfarm should hence be capable to support this, customizable via env vars just like the rest.
Configuring this on our various instance will be another issue