Add cedar slurm controller

Release notes

The computing centre "cedar" requires a container setup to run ATLAS software. A dedicated slurm submission controller provides support.

Details

The cedar controller has higher priority than the default slurm controller. It is only used if the command sbatch is available and points to the location /cvmfs/atlas.cern.ch/repo/ATLASLocalRootBase/wrappers/containers/slurm/sbatch.