[FEAT] Nix/NixOS deployment module

[batonac]

There's too much complexity inherent to the current FluxNode deployment paradigms (IMO). Sure, there are some nice scripts around, but they leave a considerable maintenance burden behind. Deployment via a Nix Flake providing a module could be an incredible boost for Flux deployments, handling the provisioning, configuration, and maintenance/upgrades of all required software packages and Flux-specific services with a modular declarative setup.

As a proof of concept, consider how easy it is to enable the "Ollama" AI service in a NixOS declarative configuration, including optional advanced configuration parameters:

services.ollama = {
  enable = true;
  acceleration = "rocm";
  environmentVariables = {
    HCC_AMDGPU_TARGET = "gfx1031";
  };
  rocmOverrideGfx = "10.3.1";
};

This small snippet is sufficient for downloading and installing the necessary software on the node, enabling the corresponding services, and configuration advanced configuration parameters. The same applies to a whole host of software and services available in the Nixpkgs archive.

In the case of a FluxNode, these configuration parameters would include Node/Account IDs, but could include other advanced overrides, like data directories, OCI runtime, etc.

Additionally, targeting NixOS Unstable (which is not as unstable as it sounds) would provide a rolling-release base for keeping nodes perpetually updated and secure.

I'd be willing to pitch in some help, but I don't have my bearings on the underlying components and how they fit together yet, and it would be really sweet if there was interest in adopting this approach upstream.