Add Ensemble notebook examples to PyCIEMSS tests

[brandomr]

This issue is to implement the ensembling that @sabinala demoed in various notebooks. These are great backend test cases to codify here as a baseline for our ensemble capability.

See https://github.com/ciemss/pyciemss/tree/sa-ensemble-eval/notebook/ensemble_eval_sa for more detail

[fivegrant]

Reopened. The E2E tests are working but we aren't using the notebook models

[fivegrant]

This issue was accidentally rewritten when it should have been a new one. Additionally, this issue is stale since we're considering adopting the knowledge-middleware model of scenario testing