[OpenStack-I18n] Changing Japanese coordinator

Hello I18n team, I'm happy to announce new Japanese coordinator Yuko Katabami san, who has been one of the most active Japanese translators for a few years. Also, for personal reasons, I don't have enough time to contribute OpenStack I18n team recently. Therefore, I think it is time to step down from I18n core member. I hope all you are doing well. Best Regards, KATO Tomoyuki