Update custom financial model dictionary input form

[bayc]

Expand custom_financial_model to use a more well-defined dictionary and utilize defaults for the default_fin_config

This PR updates custom_financial_model to use a dictionary that separates the configuration dictionary by technology. It also established default values within the code so the user does not have to supply the default_fin_config.yaml explicitly, with the one exception being the financial_parameters. This simplifies setup and more easily enables a user to update specific parts of the default financial configuration for different technologies.

Related issue

#284

Impacted areas of the software

custom_financial_model.py
Tests

Additional supporting information

This method still requires the user to specify a dictionary to use the custom financial model. In the inputs files, where we don't want to specify the input explicitly or point to a yaml file, the user will need to supply at the bare minimum a financial_parameters dictionary with both inflation_rate and real_discount_rate defined, as shown below.

financial_parameters:
  inflation_rate: 2.5
  real_discount_rate: 6.4

Test results, if applicable

Tests are passing.

[jaredthomas68]

Looks good to me