Optionalprovider: IMetadataProvideroptional provider; when supplied it (and its CurrentUser)
is honored so multi-provider callers create entities on the RIGHT server.
When omitted the global default Metadata provider is used.
Create a new, unsaved entity object for the named entity. Mirrors
Metadata.GetEntityObject<T>(entityName, contextUser).
MJ entity name (e.g. MJ: ML Models)
OptionalcontextUser: UserInforequest user — required on the server for isolation/audit
Metadata.GetEntityObject-backed IEntityFactory. Optionally bound to a specific provider for multi-provider correctness.