ListScenarioVersions
/api/scenarios/{scope}/{code}/versions
List the AsAt versions of a single Scenario definition, newest first: one entry per change,
with the version number, the AsAt datetime it was written, and the user that wrote it.
Scenarios are perpetual (AsAt-only), so a version's AsAt datetime identifies it completely:
pass it as the asAt on GetScenario to view that version, or as the scenario reference's
asAt on a valuation to price under it.