This is a mechanically generated patch to switch the documentation
jobs to use the new PTI versions of the jobs as part of the
python3-first goal.
See the python3-first goal document for details:
https://governance.openstack.org/tc/goals/stein/python3-first.html
Change-Id: I766b9d504ea24e1fadaad0d158da43012a07290a
Story: #2002586
Task: #24328
* Split out PDF building into a separate tox target
* Run HTML builder the same way as by Infra
* Omit Latex builder as it's not used
Change-Id: Idae8ce297fdcc05141749d31f343cb29ce89ca66