Activates multiple orders simultaneously in a single operation, improving efficiency when processing
large numbers of orders. Each order becomes live and effective based on its individual activation date.
This is useful for batch processing scenarios where multiple orders need to be activated at once,
such as during bulk imports or scheduled activations.

Every entry must supply OrderId and 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 per-order results, while true
queues the work and returns a job identifier that can be polled through the job status endpoints.