code: def GET_subdomain_ops(self, path_info, txid):
          
          blockstackd_url = get_blockstackd_url()
          subdomain_ops = None
          try:
              subdomain_ops = blockstackd_client.get_subdomain_ops_at_txid(txid, hostport=blockstackd_url)
          except ValueError:
              return self._reply_json({'error': 'Invalid argument: not a well-formed txid'}, status_code=400)
  
          if json_is_error(subdomain_ops):
              log.error('Failed to get subdomain operations at {}: {}'.format(txid, subdomain_ops['error']))
              return self._reply_json({'error': 'Failed to get subdomain operations'}, status_code=subdomain_ops.get('http_status', 500))
  
          return self._reply_json(subdomain_ops)
docs: Get all subdomain operations processed in a given transaction.
          Returns the list of subdomains on success (can be empty)
          Returns 502 on failure to get subdomains