init-template: Explain how to bootstrap a debian template image

We will build debian vms (oldstable/stable) from a template with some basis already set-up to avoid repeating those actions for new provisioned vm.

This action is needed to be once in a while (every debian migration to new stable for example). Still, this is worth documenting/scripting to ease reproducibility.

Related T1785 Depends on !28 (closed)

Related D1672

Test Plan

Connect to orsay hypervisor to execute:

root@orsay# cd /root/proxmox
root@orsay# ./init-template.sh 9  # build debian-9 vm
root@orsay# ./init-template.sh 10 # build debian-10 vm

(please don't use for debian 9 though, i'm using that template right now)

But you could test it with debian-10 vm template (id 10000; which is unused now):

root@orsay# qm destroy 10000
# set up your workstation with the ssh keys and public keys (cf. swh password
# store)
user@workstation$ ssh root@192.168.100.127 'hello from $(hostname)'
hello from debian-template-10

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Migrated from D1796 (view on Phabricator)