tailscale-systray: add module

[Yethal]

Description

Added module for official Tailscale systray app

Checklist

• Change is backwards compatible.

• Code formatted with nix fmt or
  nix-shell -p treefmt nixfmt deadnix keep-sorted --run treefmt.

• Code tested through nix run .#tests -- test-all or
  nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.
  • Generate a news entry. See News
  • Basic tests added. See Tests

• If this PR adds an exciting new feature or contains a breaking change.

  • Generate a news entry. See News

[Yethal]

@callumio Adding you as a reviewer since this is 90% copy-pasted from trayscale module

[khaneliman]

Could you also add a quick news entry for the new module. nix run .#create-news-entry and then just add a quick blurb

[Yethal]

@khaneliman done

[philiptaron]

I'm interested in reviewing and merging a version of this in Nixpkgs for nixos/modules/services/networking/tailscale.nix.

[khaneliman]

Might need to set outPath too, since it's being asserted in the test and not automatically being set anymore.

[Yethal]

@khaneliman now we're good