[7.4 rc fix] [doc] add missing configure Redis to use sockets
Created by: bbodenmiller
Add details from 7.2-to-7.3.md. Replaces https://github.com/gitlabhq/gitlabhq/pull/8047.
Created by: bbodenmiller
Add details from 7.2-to-7.3.md. Replaces https://github.com/gitlabhq/gitlabhq/pull/8047.