openapi-generator-cli: Use headless jre

[roberth]

Motivation for this change

• Remove unnecessary dependency on linux gui libs.
• Add a test to ease maintenance

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 119405 at cf070262 run on x86_64-linux 1

2 packages built successfully:

• openapi-generator-cli
• openapi-generator-cli-unstable

3 suggestions:

• warning: missing-phase-hooks

  installPhase should probably contain runHook preInstall and runHook postInstall.

  Near pkgs/tools/networking/openapi-generator-cli/default.nix:20:3:

     |
  20 |   installPhase = ''
     |   ^
  

• warning: unused-argument

  Unused argument: runCommand.
  Near pkgs/tools/networking/openapi-generator-cli/default.nix:1:57:

    |
  1 | { callPackage, lib, stdenv, fetchurl, jre, makeWrapper, runCommand }:
    |                                                         ^
  

• warning: missing-phase-hooks

  installPhase should probably contain runHook preInstall and runHook postInstall.

  Near pkgs/tools/networking/openapi-generator-cli/unstable.nix:20:3:

     |
  20 |   installPhase = ''
     |   ^
  

[roberth]

Rebased, ready for review and checks have passed.