Resolve "Fix missing Glossary link"

## What does this MR do?

Fixes broken links in University.

## What are the relevant issue numbers?

Closes #23332

See merge request !6880

Add more info on the new CI permissions model

From discussion in issue https://gitlab.com/gitlab-org/gitlab-ce/issues/22484

See merge request !6843

Refactor merge requests revisions docs

See merge request !6878

- A system note now appears on every push
- Replace dashes with underscores in images

[ci skip]

[ci skip]

Implement second iteration of cycle analytics - Change in data measurement

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/22458

Measure everything that happened in the given time range, not only what's been pushed to production. With the exception of the staging and production stages.

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6798