ForwardableOperationMetadata is our current solution for propagating operation metadata between operation contexts. The operation context (and really the ValidatedTenancyScope mounted on an opCtx) will soon become the source of truth for tenant domain, and so we need a way to propagate ValidatedTenancyScope between operation contexts. This ticket covers work to stash a ValidatedTenancyScope in ForwardableOperationMetadata so it can be applied to operation contexts constructed on behalf of a parent operation with tenant domain attached.