CMIP7: Ensure CDDS Prepare works with CMIP7 plugin and variable list

[matthew-mizielinski]

Expected changes:

• Interpretation of variable list
• Interaction with MIP tables
• Access to streams configuration (sub-classes of BaseStreamInfo, StreamIdentifier, StreamInfo etc)

Note: Code for interfacing with the data request is not expected to be part of CDDS Prepare for CMIP7. We will construct the variable lists separately.