Enable ssh fast lookup

Based on https://docs.gitlab.com/ee/administration/operations/fast_ssh_key_lookup.html#setting-up-fast-lookup-via-gitlab-shell it doesn't look like we were doing this correctly.

I had a couple of occurances where i couldn't pull over ssh and properly following these steps did resolve it. One main problem will be that we never restarted the ssh service after updating the config. I've also disabled the admin setting as this is what actually enables the change.