Demonstration WIP for ESNB analysis

[ceblanton]

Describe your changes

"fre analysis run" had relied on the upstream https://github.com/NOAA-GFDL/analysis-scripts repository for the base AnalysisScript and derived analysis script-specific classes that appropriately override the run_analysis method.

This framework did not align with the ESNB approach, but we can make it align with these changes

• Instead of each analysis script defining a class, each analysis type (e.g. c-shell, esnb, mdtf) will define the derived class
• Instead of keeping the derived classes in a separate package, let's keep them in fre-cli as there won't be many

Issue ticket number and link (if applicable)

Checklist before requesting a review

• I ran my code
• I tried to make my code readable
• I tried to comment my code
• I wrote a new test, if applicable
• I wrote new instructions/documentation, if applicable
• I ran pytest and inspected it's output
• I ran pylint and attempted to implement some of it's feedback
• No print statements; all user-facing info uses logging module