Switch our Jenkins ISO build system to vagrant-libvirt

Originally created by @bertagaz on #11972 (Redmine)

Being able to have reproducible builds asks to use the same build system everywhere. We should update our isobuilders and manifests to switch the ISO build process on Jenkins to the now canonical way of using vagrant-libvirt.

Feature Branch: wip/11972-use-vagrant-in-jenkins

Parent Task: tails/tails#5630

Subtasks

• #12017 (closed)
• tails/tails#12327

Related issues

• Related to tails/sysadmin#12009
• Related to #12503 (closed)
• Blocks tails/tails#11979
• Blocks tails/tails#11980