gotify-desktop: init module

[Joker9944]

Description

Add a new service module: gotify-desktop a Gotify message forward daemon.

Notable things:

• gotify-desktop does support darwin but I'm not sure how to create the systemd service equivalent for darwin. So I designed the module as linux only.
• The token option is a bit weird but is in the expected format for the service.
• Running all tests fails on a unrelated test, but all added tests run successfully.

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