Fixes #2921

Testing

1. Spin up local Browsertrix, verify seed file cleanup cron job is created with schedule set in values.yaml or local.yaml Helm chart override
2. Specify a different schedule with cleanup_job_cron_schedule in local.yaml and redeploy
3. Verify that backend logs print a message indicating the cron job schedule has been updated
4. Verify schedule was in fact updated: kubectl get cronjobs