add function to list last status of active cron jobs

[FxKu]

We want to alert on failing cron jobs. But robot_zmon user has no rights to query tables cron.job and cron.job_run_details. Even when granted USAGE and SELECT, the details are protected by a row level policy. Therefore, the PR suggests to add a wrapper function with SECURITY DEFINER to allow the invoker to list the last status of active cron jobs.

[hughcapet]

do we want this function to be accessible for all users or only for robot_zmon?

[FxKu]

all users that have access to metric_helpers schema, I would say

[hughcapet]

👍

[FxKu]

:+1: