This pull request adds the ability to both bulk get and unset configuration options on slurm config objects. This functionality will be helpful for both if we want to reset the state of Slurm, and quickly get configuration information for various Slurm objects for comparison against new information received by the charms.

For example:

slurmctld = SlurmManagerBase(ServiceType.SLURMCTLD)

# Get the entire Slurm controller configuration
slurmctld.config.get()

# Reset the configuration
slurmctld.config.unset()

Misc.

• Fixes a bug with .unset(...). If we use snap unset ... instead of snap set ..., we don't need to append the ! exclamation point to the end of the key name. Whoopsies 🥶
• ConfigurationManager now takes a string in its constructor rather than a ServiceType. This makes it much easier to create configuration managers for slurmctld components such as cgroup and acct_gather. I realized that ConfigurationManager only needs config_name, so there's no need to actually pass the full ServiceType enum.