Built in admin user should have the ability to change auto-completion via server.conf

## What?

Currently there is no way to change this in any way shape or form.

## Why?

When expensive queries are run they can sometimes make the cluster unstable on multi terabyte clusters. We used to have a way to disable auto-completion in server.conf all together for all users however there appears to be some regression and this is no longer possible. An alternative would be to modify this user alone in server.conf.