NixOS Live Image: convert to a flake

Now `nixpkgs` will be pointing to a specific release, which has a much
smaller chance to unexpectedly break. Currently 23.11. The next one will
be 24.05, 24.11, etc.

NixOS *releases* receive security updates, but packages are upgraded
conservatively, thus don't generally break. As a result, we should need
to worry about NixOS upgrades every 6-12 months. The upgrade means "bump
the version number and try to build it". If it breaks, it will generally
break only then. Less reactive, more proactive surprises.

`flake.nix` was written by @thomaseizinger in
https://github.com/drduh/YubiKey-Guide/issues/406. Changes from the
original:
- change Gnome to xfce. Now it loads with 384MB of RAM and works well
  with the simplest graphics (hello qemu).
- less nasty workaround for hopenpgp-tools. Fixed upstream
  (https://github.com/NixOS/nixpkgs/pull/279117).
- do not default `copytoram`, user can select this option in the
  bootloader.

Here is how to test it:

```
$ nix run .#nixosConfigurations.yubikeyLive.x86_64-linux.config.system.build.vm
```

*Note for the maintainer*: it would be great if you could occasionally
run `nix flake update --commit-lock-file`, *especially* after updating
github.com/drduh/config.git.

Fixes #406

Co-authored-by: Thomas Eizinger <thomas@eizinger.io>

0 files changed, 0 insertions, 0 deletions