Add print wiki page documentation
What does this MR do and why?
Add documentation for the new Print as PDF wiki feature.
Review app: https://main-ee-134025.docs.gitlab-review.app/ee/user/project/wiki/index.html#export-a-wiki-page
Related issue
Release post item MR
gitlab-com/www-gitlab-com!129427 (merged)
The doc link in this MR should be updated after this MR is merged.
Edited by Phillip Wells