More flexibility in parking configuration options

[pksohn]

The types of parking configurations, as well as their square footage and cost, are configurable in the SqftProFormaConfig object. See docstrings for those pieces here.

As explained in the docstrings, these three set parking types are hardcoded in several places in the SqftProForma code. Examples here and here.

We should explore whether it makes sense to fully parameterize and expose these functionalities to be configurable, or to leave them as three rigid types that must be selected from. If the former, we need to develop a thoughtful specification for the parking configuration - perhaps a new config object.