automate installs

right now, installing machines is mostly a manual, or semi-manual process: we install debian, preferably with crypto, and then do stuff on top.

some of it is done by hand, some is done in puppet.

we should have a standardized install process that gives us a reproducable, identical install across platforms. then Puppet is what customizes the machine on top of that.

this ticket aims at documenting what we already have and where we could possibly go. this is one of the question we answered "no" on in the "ops questionnaire" in #30881 (moved). see also the automated upgrade part in #31957 (moved).

When we started this work, the installer had this many manual steps:

new-machine (common trunk): 14 steps
new-machine-hetzner-robot: +43 steps (57 total)
new-machine-hetzner-cloud: +21 steps (35 total)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information