nixos/headscale: Add extraSettings option

[oliverwiegers]

extraSettings adds the possibility to set headscale config options that don't have a nixos module option exposed.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[oliverwiegers]

@kradalby @Misterio77 any thoughts on this change?

[kradalby]

Make sense to me, but drop the format change for the rename asserts

[kradalby]

Actually, I was a bit fast, I think we already support this? I think the settings can have unnamed things and they will be added.

[oliverwiegers]

@kradalby thanks for the review.
The format change is enforced by the CI. Without it the CI fails. This check to be specific.

Adding unnamed values to the settings option might work. What does not work is adding something to an existing sub option like settings.dns that fails.
Resulting in us being unable to specify the nameservers and other dns stuff. This will be the case with other defined sub options as well.

[oliverwiegers]

@kradalby I was mistaken. The format change was not necessary. Earlier the CI failed for another format issue. I dropped the format change

[oddlama]

Adding unnamed values to the settings option might work. What does not work is adding something to an existing sub option like settings.dns that fails. Resulting in us being unable to specify the nameservers and other dns stuff. This will be the case with other defined sub options as well.

Can you give a specific example of what is not working? As far as I can tell everything is properly exposed as a freeform settings option, so you should be able to add additional yaml at any level

[SuperSandro2000]

Yep, setting is a freeform option. You can just add anything you like to it.