Restore private.key provisioning from Vault as requested by dereckson

Apply dereckson feedback: add headers, remove defaults for bind/port to fail loudly if undefined

Just a note Flow isn't maintained anymore. The current recommended discussions extension is https://www.mediawiki.org/wiki/Extension:DiscussionTools

YAML/Jinaj Style: remove defaults to fail loudly on missing ports/bind as suggested by dereckson, plus add headers

Provisioning of /etc/anubis/private.key we added here has disappeared: https://devcentral.nasqueron.org/D3908?vs=10478&id=10480#toc

Plan is to replace pip installation by a script, ideally invokable through make, to prepare the venv or anything else with Salt there.

Proof of concept to call OVH API from Python to define MAC address to router-002/003.

Fix Anubis deployment: unify env vars, reconcile policies with P390, and align Nginx config

At this point, we can consider that the goal "create a wiki farm" is accomplished, and the subtasks are feature requests / bugs to solve in the ongoing cycle.