staging infra: Setup gateway vm

when vlan is ready:

• proxmox: Add new network interface to access new vlan + bridge
• Add new gateway vm (firewall, proxy, router) with public ip address

else (when vlan not ready):

• instantiate new vm (+ puppet)
• make it route 192.168.128.0/24 paquet to louvre

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Migrated from T1874 (view on Phabricator)