Migrate Project#owner to have OWNER membership

With !78193 (merged), new personal project owners will have OWNER membership. We need to migrate members records for existing personal projects too.

See https://gitlab.com/gitlab-org/gitlab/-/issues/351986#note_831687602 for numbers as of 2022/02/04.

Overall strategy

• Get all personal namespaces and their memberships
• Create a membership for any users that are OWNER via owner_id
• Change MAINTAINER memberships to OWNER