Out of disk space on prometheus storage

The partition used to store the prometheus storage is almost full

vsellier@pergamon /var/lib/prometheus/metrics2
 % df -h .
Filesystem      Size  Used Avail Use% Mounted on
/dev/vdc1       246G  228G  5.9G  98% /var/lib/prometheus

The disk should be extended to avoid a disruption of service

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Migrated from T2859 (view on Phabricator)