Creates an export and its destination atomically. The organization is
taken from the API key; the project_id in the body must belong to it,
as must the destination's integration_id. The export name must be
unique within the project. For a weekly schedule, run_day_of_week
is required.

Include additional_destinations to deliver to more than one
destination from the start; each entry is the same destination shape as
destination and is written in the same transaction. Only valid
alongside destination; an export can have at most 5 destinations
total, each on a different connection. Marketplace destinations
cannot be combined with others, and a DelivrDSP destination can only be
the export's first (primary) destination.