Refactor nersc class

[dylanmcreynolds]

The nersc class in https://github.com/als-computing/splash_flows_globus/blob/main/orchestration/nersc.py acts as a client for using the NERSC SFAPI. Unfortunately, it contains code specific to ptychography. There could be many many use cases for this class. Let's refactor it so that it is more generic, and can be used by any prefect flow that wants to make calls to the SFAPI.