Every entry must supply OrderId, at least one order line item identifier, and a
ReadyForActivationDate; the whole request is rejected with 400 Bad Request if any entry is
incomplete.

Unlike the single-order activate endpoint, isAsync is honoured directly here:
false processes the activations in the request thread and returns the outcome per order, while
true queues the work and returns a job identifier that can be polled through the job status
endpoints.

Note that this endpoint is routed at /orders/orderlineitems/activate and is not scoped to a
single parent order, since each entry names its own order.