WIP: Develop/submit clusters

[bpatel2107]

Added Cluster object and ability to submit individual pyro objects to a cluster
Currently SLURM schedulers are supported.

TODO:

• Need to add CGYRO and GENE method for a run_command
• Add PBS scheduler
• Set base directory for gk_code binary
• Add submission for PyroScan object either as
  • One job for whole scan
  • One job for each run in scan

[d7919]

It might be useful to look at existing tools such as https://fabsim3.readthedocs.io/en/latest/ which it might be possible to build on top of.