Merge EE doc/​user/​project/​issues to CE

Description

Merge EE doc/​user/​project/​issues to CE

MR workflow

The following are stuff we gathered during our MR tests (e.g., https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21089) (if you find something that needs to change, comment in &199 (closed)):

1. Locally copy the EE dir to CE
2. Create MR
3. Using our documented EE/CE doc alignment standards:
   1. Convert URLs to relative URLs. If a link fails the check because it does not exist yet in CE (from another to-be-merged section) keep absolute URL. We’ll do a find/replace later.
   2. If a feature was only in EE and had no tier-specific badge, look up the feature and add one. If any question, ask relevant PM.
4. Create EE equivalent MR