[RFC] PVE installer: GRUB PXE and Foreman/Satellite integration

[Alex Harvey <alexharv074@gmail.com>]

Hi all,

I am working on automated Proxmox VE installation in an environment managed
by Foreman / Red Hat Satellite.

The current POC uses Satellite for DHCP, TFTP and iPXE provisioning. It
requires two workarounds:

* A custom answer adapter translates the installer’s HTTP POST into
  Foreman’s /unattended/provision?mac=<MAC> request.
* iPXE supplies the prepared ISO as an initrd. This works there, but is not
  suitable as the basis for reliable GRUB PXE boot with a production-sized
ISO.

Note also that support for iPXE is deprecated in Satellite.

I opened these related enhancement requests:

* https://bugzilla.proxmox.com/show_bug.cgi?id=7990
  GRUB PXE installation media without loading the full ISO as an initrd
* https://bugzilla.proxmox.com/show_bug.cgi?id=7991
  Generate GRUB PXE configuration from proxmox-auto-install-assistant
* https://bugzilla.proxmox.com/show_bug.cgi?id=7992
  Native answer-file retrieval from Foreman/Satellite

Before attempting patches, I would appreciate guidance and feedback on the
proposed
design:

1. Would support for `--pxe-loader grub` be welcome?
2. If so, would there be a preferred way for a GRUB PXE boot to provide the
prepared
   installation medium without GRUB loading the full ISO as an initrd?
3. Would a Foreman-compatible answer file fetch mode, using the
provisioning NIC
   MAC to retrieve a host-specific answer file, be acceptable?

Many thanks,
Alex Harvey