Add university content

## What does this MR do?

Imports gitlab-org/University content into doc/university to deprecate university.gitlab.com and access it from doc.gitlab.com/universtiy.

## Are there points in the code the reviewer needs to double check?

That there are no broken links.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added

## What are the relevant issue numbers?

#22449

See merge request !6520