Host minimal profile

[vilvo]

• imported and tested minimal profile on host for NVIDIA Orin AGX
• documented the ADR proposal for the minimal host

[brianmcgillion]

Is this really the minimal we want? This is minimal for a generic headless device, I envisaged us creating minimal-minimal.nix, or barely-enough-to-boot.nix profiles, which we could contribute back.

[vilvo]

Is this really the minimal we want? This is minimal for a generic headless device, I envisaged us creating minimal-minimal.nix, or barely-enough-to-boot.nix profiles, which we could contribute back.

This is only an iteration towards that target most_minimal+hardened with testing of the profile import on NVIDIA Orin AGX target. There's hardened profile already in Nix but I did not dare to propose that yet as I'm expecting hardened-profile to break more.

Not sure if you noticed the other commit message on details of reducing the image size and # packages. That would give already some benefits for early development from this iteration.

* Use NixOS minimal profile on host instead of default
  to match the design target of minimal trusted computing
  base (TCB).
* Metrics on nvidia-jetson-orin:
  * reduces the image size and root-partition used size
    with 500M from 4.2G to 3.5G and 2.6G to 2.1G respectively
  * Number of pkgs in /nix/store from 707 t0 526
* Numbers not seen on x86 VM target as the nix-store of the
  host is mounted to the VM. Not imported on x86 QEMU target.

Given this is only a minimal iteration towards the target we have options of:

• taking this into use early (merge) and enable other profiles for other development needs with additional build targets
• postpone this PR, continue analysis of extra content in minimal profile and based on that continue development of the most_minimal+hardened-profile we could contribute back.