Docs new index for project's settings
See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html
What does this MR do?
Adds new doc index to project's settings.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/35719
Note: branch created from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13545's, which needs to be merged before this.
Edited by username-removed-236961