[Enhancement]: Use jwtctl to get/set/generate the JWT signing key used by Slurm

[NucciTheBoss]

PR #34 adds an initial implementation for JWT signing key management that uses the cryptography module as the backend for generating the signing key. However, in the future, we want to use a tool similar to mungectl to manage the JWT key so that we aren't entirely reliant on slurm_ops to manage the key. This also makes it much easier to proxy in external compute nodes as they can have the same interface as the Slurm daemons managed by the Slurm charms.