Update the configuration for CMAQ and WRF

[crdanielbusch]

The motivation

It will be easier for future users to create a correct configuration file if we define the requirements for the individual entries and types in detail and include them in the documentation.

The proposed solution

• [x] Store the requirements for the configuration in the docstring of the CMAQConfig and WRFConfig Class
• [ ] Update the docstring in the class definition according to the latest requirements
• [ ] Test what is the appropriate type for each variable

[lewisjared]

Also the NCI configuration for the CMAQ setup should be extracted to JSON file as a starting point for NCI users