in src/main/scala/com/gu/zuora/fullexport/Impl.scala [191:197]
def discoverFields(objectName: String): List[String] = {
logger.info(s"Auto-discovering field names of $objectName...")
val rawXml = describe(objectName)
val fieldNames = getFieldNames(rawXml)
val relatedObjectIds = getRelatedObjects(rawXml).map(objectName => s"${objectName}.Id")
fieldNames ++ relatedObjectIds
}