Implement chunks builtin for makeDerivationParallel

[dsalaza4]

makeDerivationParallel is great for local parallelization in just one machine.

Many times, the next step for improving performance is distributing workloads into several machines.

A chunks builtin would be great for this:

{
  chunks,
  inputs,
  makeDerivation,
  makeDerivationParallel,
}: let
numbers = [0 1 2 3 4 5 6 7 8 9];
myChunks =  chunks numbers 3; # [[0 1 2 3] [4 5 6] [7 8 9]]

buildNumber = n: makeDerivation {
  name = "build-number-${n}";
  env.envNumber = n;
  builder = ''
    echo "$envNumber"
    touch "$out"
  '';
};
in
  makeDerivationParallel {
    dependencies = builtins.map buildNumber (inputs.nixpkgs.lib.lists.elemAt myChunks 0);
    name = "build-numbers-0";
  }

With this logic one would be able to easily distribute workloads into several CI jobs, achieving distributed parallelization.