Update metrics extraction for swh-scrubber v2
Adapt the SQL query for the swh_scrubber_coverage metrics and add a new swh_scrubber_ongoing_check one giving some insight on the currently running checks.
Staging instance, all changes can be removed at any time
Adapt the SQL query for the swh_scrubber_coverage metrics and add a new swh_scrubber_ongoing_check one giving some insight on the currently running checks.