Add editor for cgroup.conf file

[NucciTheBoss]

The cgroup.conf file is used by Slurm to configure Linux cgroup-related functionality. This is necessary for job tracking and orchestration in Slurm, so we should really support accessing and editing this file.

Manual page: https://manpages.ubuntu.com/manpages/noble/en/man5/cgroup.conf.5.html

[NucciTheBoss]

Related PR: charmed-hpc/slurmutils#19. Only took a hot minute 😅

[NucciTheBoss]

@jamesbeedy PR for cgroup.conf editor has been merged. Haven't published to PYPI yet because there are some other small updates that I would like to merge before bumping to version 0.7.0, but the cgroup.conf editor supports all the major options outlined in the cgroup.conf manpage: https://manpages.ubuntu.com/manpages/oracular/en/man5/cgroup.conf.5.html