[Proposal] Add headlight mode to autoware_auto_msg.

[zhiwango]

Hello

We are developing a self-driving car, hoping to control the position light and headlight flashing and get the status of a headlight.

But now, only DISABLE, ENABLE_LOW, and ENABLE_HIGH are for headlight command and status.

Can you add POS and FLASH mode to autoware_auto_vehicle_msgs in autoware_auto_msg?

Thanks.

[zhiwango]

こちらの件をチーム内で検討しましたが、現在AutowareからHeadlightのPOS, FLASHを制御する要望が来てなくて、一旦現状維持します。（POS, FLASHはENABLE_LOWと紐付けにする）

Thanks!