Feature/accf metrics

[trdean1]

Changes

Adds now optional output that expresses forcing in both global averaged RF and ATR20

Internals

Adds two new parameters to CoCipParams: compute_atr20 (false by default) and global_rf_to_atr20_factor (0.0151 by default Global averaged RF is converted by taking EF (J) and dividing by the surface area of the earth (m^2) and the number of seconds in year, to give equivalented delta in global RF over a year needed to capture the same amount of energy. A constant multiple converts this to ATR20. test_eval_persistent sets compute_atr20 and static test values are updated to include new outputs

Tests

• [x] QC test passes locally (make test)
• [x] CI tests pass

Reviewer

@zebengberg @thabbott