cron_schedule isn't optional as stated in the docs

[AugustoEMoreira]

The documentation states that the field cron_scheduler is optional. This is not true.

I bet this is true for saved searches as reports, but it is definitely not true for all use cases.

Properties in use:

 is_scheduled = true
 dispatch_earliest_time = "rt"
 dispatch_latest_time = "rt"
 actions                    = "slack"
 alert_severity             = "3"
 action_slack_param_channel = "#redacted"
 action_slack_param_message = redacted