zerotier: add zerotier-systemd-manager AND corresponding service option

[x-zvf]

This pr packages zerotier-systemd-manager and provides the option services.zerotierone.generateSystemdNetworkdConfig to automatically invoke it after service start. The corresponding services.zerotierone.systemdManagerPackage is also added, to be able to specify the package of the tool.

Usage of this tool is necessary (if avoiding manual configuration) to have working DNS resolution for zerotier DNS records when using systemd-networkd.

Things done

• Built on platform(s)
  • [X] 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
• [X] Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• [X] 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
• [X] Tested basic functionality of all binary files (usually in ./result/bin/)
• Nixpkgs 25.11 Release Notes (or backporting 24.11 and 25.05 Nixpkgs Release notes)
  • [ ] (Package updates) Added a release notes entry if the change is major or breaking
• NixOS 25.11 Release Notes (or backporting 24.11 and 25.05 NixOS Release notes)
  • [ ] (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
• [X] Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other contributing documentation in corresponding paths.

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Add a :+1: reaction to pull requests you find important.

[x-zvf]

I am not sure who to contact when adding a package, so I am pinging the maintainers of the zerotierone package.

@sjmackenzie @zimbatm @ehmry @obadz @danielfullmer @mic92

[x-zvf]

@Prince213 Can you remove the "needs-changes tag" then?

[zimbatm]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 417102 Commit: e64f6b49ffa3d1df3ffbb1123b7109bbf1a3b147

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x86_64-linux

:fast_forward: 2 packages blacklisted:

• nixos-install-tools
• tests.nixos-functions.nixos-test

:white_check_mark: 1 package built:

• zerotier-systemd-manager

[x-zvf]

But if this is too controversial, I'll remove the service commit and then merge just the package for now.

[x-zvf]

@zimbatm What should it be?