nixos/tailscale-auth: restart on-failure and wait for tailscaled

[bouk]

I observed the following:

Mar 25 11:01:59 systemd Started Tailscale NGINX Authentication service.
Mar 25 11:01:59 (inx-auth) tailscale-nginx-auth.service: Failed to set up mount namespacing: /run/tailscale/tailscaled.sock: No such file or directory
Mar 25 11:01:59 (inx-auth) tailscale-nginx-auth.service: Failed at step NAMESPACE spawning /nix/store/gzlgb9bxxzikif2r6hllvgnr7gjqrrl3-tailscale-nginx-auth-1.80.3/bin/tailscale.nginx-auth: No such file or directory
Mar 25 11:02:00 systemd tailscale-nginx-auth.service: Main process exited, code=exited, status=226/NAMESPACE
Mar 25 11:02:00 systemd tailscale-nginx-auth.service: Failed with result 'exit-code'.

This happened while updating, because the service started before tailscaled was available. It also didn't restart after the failure. Here I'm adding a restart on-failure and making it start after tailscaled

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)
  • 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
• 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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