Sets the imeis associated with a task schedule.
The list of devices can be empty, signaling that there will be no devices associated with the task schedule.

For repeating usage-based schedules, every device carries the starting value matching the
schedule's repeat type: startingActiveHours when the schedule repeats by intervalActiveHours,
startingOdometer when it repeats by intervalOdometer. Date-based and one-time schedules take
imei-only entries. Omitting the field keeps the value already stored for that device; an
explicit null clears it.