Make Slurm client-side commands available on compute nodes

[NucciTheBoss]

Currently we don't install the Slurm client-side commands — sinfo, srun, sbatch, etc. — on the Charmed HPC cluster compute nodes. While this is fine for workloads that do not need to wire back into Slurm, it can hinder workloads that resubmit themselves as job arrays or use srun to kick off MPI processes. We should install these commands when we deploy the slurmd operator so that they can then be used within user workloads.

Required changes

The required changes for installing the slurm-client package on slurmd units is quite small. We just need to add slurm-client to the list of packages to install in _AptManager from hpc-libs:

https://github.com/charmed-hpc/hpc-libs/blob/685dee7e864635986ce01228bf4258be2418b49d/lib/charms/hpc_libs/v0/slurm_ops.py#L656-L657

We'll need a vbump for hpc-libs, but the required changes are quite easy.