Remove cockpit

[sjpb]

Removes the cockpit-ws package which removes the MOTD:

Activate the web console with: systemctl enable --now cockpit.socket

Fixes #377.

The base branch was changed.

[sjpb]

Following checks carried out on a RL8 Azimuth cluster using:

azimuth_caas_stackhpc_slurm_appliance_git_version: fix/motd
azimuth_caas_stackhpc_slurm_appliance_image: bdbf80eb-6182-4de7-b430-7d3b8e798e22 # openhpc-RL8-240327-1050-4812f852
admin_dashboard_ingress_basic_auth_password: $secret

• OOD shell: OK, no message
• OOD desktop: OK, inc modules
• OOD jupyter: OK
• OOD files: OK
• monitoring: OK