Docs: new admin index
Same as https://gitlab.com/gitlab-org/gitlab-ce/issues/39688, including EE features:
-
Cherry pick CE https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15724 to EE -
Add EE-only stuff
[https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3664]
Edited by Marcia Ramos