gitkraken: add desktop entry

[winniequinn]

Motivation for this change

A desktop entry is always nice for a desktop application like GitKraken! Most other Linux distributions that package GitKraken already have a desktop entry.

Note: The tarball does not contain an icon so switched over to using the dpkg.

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[mention-bot]

@winniequinn, thanks for your PR! By analyzing the history of the files in this pull request, we identified @globin to be a potential reviewer.

[winniequinn]

I believe @xNWDD may wish to review this as well.

[xNWDD]

Reviewed points

• package built on sandboxed x86_64 Nix
• icon showing properly on fully clean xfce4
• executable basic functionality tested on x86_64 Nix

Comments

Because of my tiling addition I didn't even think about the icon xD
But I can see this is a great improvement for most desktop users.