code: public function addDomainCacheRule($domain, $rule)
      {
          return json_decode(self::getClient()->addDomainCacheRule($this->sn, $domain, $rule));
      }
docs: Add a cache rule to domain $domain
  
  @param string $domain
  @param array $rule (required keys are 'cacheType','ttl','fileMatch','fileType' see official doc at https://api.ovh.com/console/#/cdn/%7BserviceName%7D/domains/%7Bdomain%7D/cacheRules#POST)
  @return mixed