Initialize the process of switching to a new set of LLM datasets

This endpoint will be called at the beginning of the batch operation updateLLm. It will signal the LLW service to start queuing the update requests so that they can be replayed towards the new LLW datasets after they are created by the updateLLM job. This endpoint will block until all non-queued in-progress LLW updates are finished to ensure that all future updates will be queued once the method returns.