ocamlPackages.buildDunePackage: deprecate useDune2

- It uses the `fetchFromGitHub` fetcher to get its source.

- `duneVersion = "2"` ensures that Dune version 2 is used for the

  build (this is the default; valid values are `"1"`, `"2"`, and `"3"`);

  note that there is also a legacy `useDune2` boolean attribute:

  set to `false` it corresponds to `duneVersion = "1"`; set to `true` it

  corresponds to `duneVersion = "2"`. If both arguments (`duneVersion` and

  `useDune2`) are given, the second one (`useDune2`) is silently ignored.

- It also accept `duneVersion` parameter (valid value are `"1"`, `"2"`, and

  `"3"`). The recommended practice it to set only if you don't want the default

  value and/or it depends on something else like package version. You might see

  a not-supported argument `useDune2`. The behavior was `useDune2 = true;` =>

  `duneVersion = "2";` and `useDune2 = false;` => `duneVersion = "1";`. It was

  used at the time when dune3 didn't existed.

- It sets the optional `doCheck` attribute such that tests will be run with

  `dune runtest -p angstrom` after the build (`dune build -p angstrom`) is

buildDunePackage rec {

  pname = "angstrom";

  version = "0.15.0";

  duneVersion = "2";

  minimalOCamlVersion = "4.04";

  pname = "wtf8";

  version = "1.0.2";

  useDune2 = true;

  minimalOCamlVersion = "4.02";

  src = fetchurl {

{ pname, version, nativeBuildInputs ? [], enableParallelBuilding ? true, ... }@args:

let Dune =

  let dune-version = args . duneVersion or (if args.useDune2 or true then "2" else "1"); in

  let dune-version = args.duneVersion or "2"; in

  { "1" = dune_1; "2" = dune_2; "3" = dune_3; }."${dune-version}"

; in