Show list of built guides instead of "We are sorry"

[maximiliankolb]

URL: https://docs.theforeman.org/nightly/Managing_Security_Compliance/

I wish it would just redirect to https://docs.theforeman.org/nightly/Managing_Security_Compliance/index-katello.html, but I know that's not working for everyone.

Task: Instead of showing a note "We are sorry ...", we should show all three/five built guides:

{Team} builds upstream documentation for different scenarios:

* Foreman on Enterprise Linux: https://docs.theforeman.org/nightly/Managing_Security_Compliance/index-foreman-el.html
* Foreman on Debian/Ubuntu: https://docs.theforeman.org/nightly/Managing_Security_Compliance/index-foreman-deb.html
* Foreman+Katello: https://docs.theforeman.org/nightly/Managing_Security_Compliance/index-katello.html