[FR] Implement container internal cronjob via k8s CronJob

[d7oc]

Right now we still use the crond started in the container itself to executed jobs periodically.

This feature request is about the implementation of this mechanism via the CronJob implemented in k8s: https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/

Note: We need to find a way to execute the job in the container without the triggering any updated of the oC system.

[d7oc]

This FR is also required for OpenShift as the cron setup in the container fails due to a permission error:

 owncloud {"level":"error","error":"failed to render template /etc/templates/owncloud.cron.tmpl: failed to open output file '/etc/cron.d/owncloud' for writing: open /etc/cron.d/owncloud: permission denied","time":"2023-06-15T16:30:37Z"}

So

owncloud:
  crondEnabled: false

has to be set to make the container start at all on OpenShift (tested with 4.13), which will disable cron.