Download export file

Export contacts in a 3-stage process:

(1) Filter and choose which contacts to export using POST /contacts/exports - works like POST /contacts/search with filtering, returns the UUID of the export record.

(2) Check export status using GET /contacts/exports/{id} - status can be INITIATED, PROCESSING, PROCESSED, or FAILED.

(3) Download the file using POST /contacts/exports/{id}/download - returns the URL of the file in the url field that can be fetched using a simple HTTP GET request.

This is Stage 3 of 3: Download the file.