Add back PEM power split optimization

[johnjasa]

Add back PEM power split optimization

Earlier versions of H2I included files that performed an optimal power split for electrolyzer stacks.
These were contained within the run_PEM_master.py file under optimize_power_split.
Initially noted here: #384 (comment)

Proposed solution

Add back the power split logic and integrate it with the current H2I framework.

Alternatives considered

Additional context