Added more detail to the sg server rollout process
Created by: Joelkw
Questions around the sourcegraph server rolllout process came up in the Search Team sync meeting Monday and we realized we needed to update the handbook to provide more detail. (Link to sync meeting item: https://docs.google.com/document/d/1QbyXbNlCWCgy7YHqt7ETHUVongPLBJTzj_5pnfWIg0Y/edit?disco=AAAAG8aHGsg the notes.) Confirmed with @christinaforney this reflects the current process.