Fetch the list of available time slots.
    Time slots cannot be booked once the referral is confirmed.
    Before calling this endpoint, body parts and an imaging provider must have been selected.
    The list of body parts determines how long the time slots need to be.
    Each time slot is divided in 15 minutes blocks of time.
    Each 15 minute block has an ID.
    For example, for a 30 minutes time slot, you would need to book 2 IDs.