Download an export that you've created specified by
id. Obtain an
id from Create Custom Export.
file_url will return an HTTP 404 until
finished. You may decide to poll this endpoint until the file is ready.
file_url will expire 1 week from creation. This is to ensure that your exports are up to date.
NOTE: id vs. template_id
idrefers to the id of this export, whereas
template_idrefers to the source template. You'll use
idto GET the export that you've created.