Get the amount owed for demurrage charges through a specific date.

This endpoint calculates demurrage charges based on container_number and mbl_number instead of
requiring a container UUID. It calculates existing charges plus projected future charges
through the specified date.

This endpoint requires that the container has a valid demurrage_paid_through_date set.
If the container is still in transit (hasn't been discharged), this endpoint will
return a 400 error as demurrage calculation is not possible yet.