add contrib pkg (centos7)

Folowing: https://community.france-bioinformatique.fr/t/seff-commande-introuvable/

Seff was install previously on login1 (https://gitlab.com/ifb-elixirfr/cluster/ansible/-/merge_requests/565), but not on login2.

Merge request to install slurm contrib on client nodes. Packages are only availble on CentOS.