Bulk create audiences

Create up to 25 composition audiences in a single request. Each item wraps one or more pre-existing segments (any subtype — filter, matched, similarity, or propensity) via segment_ids/excluded_segment_ids or segment_refs; it does not create new segments. To generate a new matched/similarity/ propensity segment and its wrapper audience in one call, use POST /v1/segments with create_audience: true instead. Optionally links all created audiences to a campaign via the audience_links sub-collection. An unknown campaign_id returns 400 INVALID_CAMPAIGN_ID and nothing is created. An item that references a segment that does not exist, is deleted, or is not accessible is not created and is reported in errors. Requires 'creator' scope.