Updated PEM cell modeling schema

[elenya-grant]

Almost ready to be merged - one test still fails and is expected to (further information below). Further updates are potentially needed to the example scripts.

Feature or improvement description
Updated the modeling schema for PEM_cell to remove hard-coded model parameters such as electrode pressures, membrane thickness, faradaic coefficients, and removed dryer losses.

Impacted areas of the software

primary updates to PEM_cell.py and modeling_schema.yaml. Relevant tests were also updated.

Additional supporting information

Primary PEM cell modeling parameters and operational conditions that were previously hard-coded are now included in the input file. Previous hard-coded modeling parameters are now the default values in modeling_schema.yaml.

Test results, if applicable

• LCOH test is expected to fail - didn't update data frame values. LCOH tests need to be revised. Fails because more H2 production since dryer loss was removed.
• Any tests related to H2 production rate have been updated to reflect H2 production without dryer losses. Dryer losses should be included in BOS modeling and not electrolyzer cell.
• default test values reflect the previous hard-coded numbers.