Multi-instance and NBFB testing capabilities

We adopt MVK testing for now.

MVK testing

In Multivariate Kolmogorov-Smirnov (MVK) test, an ensemble of multi-year runs with the 2 versions of the code to check that the climate statistics of important variables are unchanged between ensembles.

For some background, see DOIs:

- 10.1145/3324989.3325724
- 10.1145/3468267.3470572

Multi-instance testing

See following link for background on the multi-instance capability in CIME.

Link

In SCREAM/EAMxx, it works in exactly the same except that the namelist file has a different name and location. Instead of user_nl_eam and atm_in for EAM, in SCREAM, we do not use user_nl_scream at all (even though it will be there) and we rely on run/data/scream_input.yaml.

Thus, much like the original implementation in other components, the user must specify their choice of settings in the corresponding input files, namely scream_input.yaml_0001, and so on.

Together

For MVK testing to work, it relies on the multi-instance capability. We use the default MVK test to instantiate a new MVKxx test in components/eamxx/cime_config/SystemTests. In the test definition, we must edit the scream_input.yaml specs.