Docs: fix duplicate sections (CI docs)
See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html
What does this MR do?
- Delete duplicate sections on EE-docs (prob originated by merge conflicts on the CE > EE upstream):
- Link CI doc to admin doc (backport to CE)
- Move sections for better reading flow (backport to CE)
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/41138 and https://gitlab.com/gitlab-org/gitlab-ce/issues/41872
Edited by 🤖 GitLab Bot 🤖