code: public function installOperatingSystemUnattended($vpsName, $operatingSystemName, $base64InstallText)
      {
          return $this->call(self::SERVICE, 'installOperatingSystemUnattended', [$vpsName, $operatingSystemName, $base64InstallText]);
      }
docs: Install an operating system on a vps with a unattended install file.
  
  @param string $vpsName             The name of the VPS
  @param string $operatingSystemName The name of the operating to install
  @param string $base64InstallText   base64_encoded preseed/kickstart text
  
  @throws \SoapFault
  
  @return mixed