Docstrings

[kdayday]

This is the second part of PSY docstrings updates:

• Changes are focused on src/descriptors/power_system_structs.json to fill gaps and update the top-level docstrings and argument descriptions in the Model Library
• Optional and "do not modify" arguments are identified
• A glossary has been added in the Modeler Guide and some cross-references have been added. There's more we could do there or reformat, particularly with the dynamics acronyms, and some terms are still undefined.
• HybridSystem isn't added to the documentation yet (I can't remember if someone else was working on that) Added HybridSystem docs
• Made cost documentation visible in the Modeler Guide and Model Library, but haven't resolved any to-dos left by Gabriel
• Docs build is attached
• Edit: Includes renames to RenewableNonDispatch, ProductionVariableCostCurve, ConstantReserve, ConstantReserveGroup, ConstantReserveNonSpinning, and moves ControllableLoad to be a StaticLoad

build_PSY.zip

[rodrigomha]

I'm merging this to a dev psy4 branch (kdrh/psy4_docs_renaming) to start cleaning the other repos with the names changes.