[SURE-9724] Elemental provisioning behaviour

[kkaempf]

SURE-9724

Issue description:

Continuation of threads here and here

We've been investigating Elemental to deploy our bare metal rke2-on-slemicro nodes recently, and I've observed some behaviour that is, counter-intuitive.

The main unanswered issue they have is to do with cloud-config in a MachineRegistration:

If they define it as cloud-config, it works as-is
If they define it in the initramfs yip stage, it doesn’t appear to get applied

I did see on this page that installation hooks aren’t run in MachineRegistration, but the customer pointed out that initramfs isn’t listed as an installation stage.
Is it expected that only boot and after-install-chroot stages would run in MachineRegistration? Would that then mean that the docs need updating?
 
And a related area they'd like clarified:

when the install process is happening and the MachineRegistration content is deployed (into /tmp/elemental/91_config.yaml I think it is) –
regardless of what’s in that section of the CR, it’s being parsed as cloud-config, not yip. That file always has #cloud-config at the top, so if
it’s valid yip, nothing at all gets processed.