Archive Katello documentation for 3.17, 3.18, and 4.0

[ianballou]

Essentially all Katello docs on theforeman.org should be converted to PDFs and archived since the documentation has been moved to docs.theforeman.org.

Older versions of Katello docs have been turned into PDFs: https://theforeman.org/plugins/katello/legacy/index.html

I had an old PR to do this for 3.17 and 3.18, but something was wrong with the PDFs and I haven't had time to get back to it: #2026

In my previous PR, I used the following: https://github.com/theforeman/theforeman.org/tree/gh-pages/plugins/katello/legacy