Facilitate comparison with FATES runs

[wwieder]

New feature type

New infrastructure or infrastructure enhancement

What is this new feature?

FATES development may be facilitated by comparison with results from the 'big-leaf' model.
The challenge here is that some variables have different names and units: e.g.

• FATES_GPP (kg/m2/s) = GPP (gC/m2/s)

Comparisons for FATES vs. FATES runs would be simple enough to add variables to ldf_variable_default, but comparisons for FATES vs. Big-leaf runs may be a bit more challenging. What the's best way to address this? Options could include a:

1. Pre-processing step that uses the time-series generation in LDF to rename variables and change units, basically converting FATES_GPP into GPP;
2. Helper script that uses a FATES flag the config file to define when a case may need unit and variable name conversions;
3. Another option I haven't considered.

@adrifoster, @samsrabin, @slevis-lmwg I wonder if you have thoughts here?

Assistance required?

No, I will make a PR when the feature is ready

Extra info

No response

[slevis-lmwg]

For now I will just mention for future reference, that the updated SpinupStability script shows three fields with their corresponding FATES names and unit conversions:
https://github.com/ESCOMP/CTSM/pull/3776/changes