[openstack-helm] Nominate Sergiy Markin as a core reviewer

Hi Openstack-Helm team, I would like to nominate Sergiy Markin as a core reviewer for the project. He's been doing many reviews recently [1]. He also contributed some Mariadb and ingress related improvements. Besides that he has wide experience in Airship which is historically closely related to Openstack-Helm. I believe we as a team will benefit a lot from Sergiy being a core team member. [1] https://www.stackalytics.io/report/contribution?module=openstack-helm-group&project_type=openstack&days=60 -- Best regards, Kozhukalov Vladimir