Rename Omnibus Praefect item
Related to: omnibus-gitlab!4980 (merged), renames "Praefect" (which was the name of Gitaly Cluster, but is not just the name of a part of it) to "Gitaly Cluster" on the Omnibus global menu.
Related to: omnibus-gitlab!4980 (merged), renames "Praefect" (which was the name of Gitaly Cluster, but is not just the name of a part of it) to "Gitaly Cluster" on the Omnibus global menu.