Bring back customizing the system config to include in the tarball

[terlar]

This was previously implemented in #260, but lost in the migration off the installer tarball.

[K900]

Generally, I'd probably prefer to have a more generic mechanism of just adding arbitrary files, similar to what make-system-tarball.nix does. We can then use that mechanism to include the default config and provide user-level overrides.

[terlar]

I updated according to your comments. That might be a good idea, but I'm not entirely sure how you would like that implemented.

I don't personally see any value in combining custom configuration with the default configuration. As soon as you add your own custom configuration via wsl.tarball.configPath you don't need the defaults, also it is quite flexible, you can have use any method to work with Nix sources to construct the configuration.

Perhaps the current defaultConfig (if generated a directory instead) could be the default value of configPath.

[K900]

It's not necessarily about custom configuration - it's about adding arbitrary files in general, like secrets or SSH keys or whatever.

[terlar]

You mean generally in the tarball filesystem? Or specifically inside /etc/nixos (what this is mainly about).

I guess there is also a case of being able to configure arbitrary commands being executed in the script. Having a configuration to add steps and their actions. I guess for example if you are planning to use flakes the part of channels is unnecessary. But I think that is a bigger topic.

[K900]

I mean in the tarball in general, see make-system-tarball.nix in nixpkgs for example.

[SuperSandro2000]

@nzbr @K900 can you take a look, please?

[nzbr]

I mean in the tarball in general, see make-system-tarball.nix in nixpkgs for example.

I'll merge this as-is and make a new issue to add something like extraCommands