* feat: save CNAME into archival data format When a DNSResponse contains a non-empty CNAME, we include it into the related list of answers. Closes https://github.com/ooni/probe/issues/2227 * doc: add design note While there, make code more compact and robust to a case where we're going to extract additional answers. * doc: document the expected growth of extraction function Based on feedback by @DecFox