build: replace changelog-d with local script

hacking changelog-d to support not just github but also forgejo and
gerrit is a lot more complicated than it's worth, even moreso since
the entire thing can just as well be done with ~60 lines of python.
this new script is also much cheaper to instantiate (being python),
so having it enabled in all shells is far less of a hassle.

we've also adjusted existing release notes that referenced a gerrit
cl to auto-link to the cl in question, making the diff a bit bigger

closes https://git.lix.systems/lix-project/lix/issues/176

Change-Id: I8ba7dd0070aad9ba4474401731215fcf5d9d2130

misc/changelog-d.cabal.nix

@@ -1,31 +0,0 @@
-{ mkDerivation, aeson, base, bytestring, cabal-install-parsers
-, Cabal-syntax, containers, directory, filepath, frontmatter
-, generic-lens-lite, lib, mtl, optparse-applicative, parsec, pretty
-, regex-applicative, text, pkgs
-}:
-let rev = "f30f6969e9cd8b56242309639d58acea21c99d06";
-in
-mkDerivation {
-  pname = "changelog-d";
-  version = "0.1";
-  src = pkgs.fetchurl {
-    name = "changelog-d-${rev}.tar.gz";
-    url = "https://codeberg.org/roberth/changelog-d/archive/${rev}.tar.gz";
-    hash = "sha256-8a2+i5u7YoszAgd5OIEW0eYUcP8yfhtoOIhLJkylYJ4=";
-  } // { inherit rev; };
-  isLibrary = false;
-  isExecutable = true;
-  libraryHaskellDepends = [
-    aeson base bytestring cabal-install-parsers Cabal-syntax containers
-    directory filepath frontmatter generic-lens-lite mtl parsec pretty
-    regex-applicative text
-  ];
-  executableHaskellDepends = [
-    base bytestring Cabal-syntax directory filepath
-    optparse-applicative
-  ];
-  doHaddock = false;
-  description = "Concatenate changelog entries into a single one";
-  license = lib.licenses.gpl3Plus;
-  mainProgram = "changelog-d";
-}

misc/changelog-d.nix

@@ -1,31 +0,0 @@
-# Taken temporarily from <nixpkgs/pkgs/by-name/ch/changelog-d/package.nix>
-{
-  callPackage,
-  lib,
-  haskell,
-  haskellPackages,
-}:
-
-let
-  hsPkg = haskellPackages.callPackage ./changelog-d.cabal.nix { };
-
-  addCompletions = haskellPackages.generateOptparseApplicativeCompletions ["changelog-d"];
-
-  haskellModifications =
-    lib.flip lib.pipe [
-      addCompletions
-      haskell.lib.justStaticExecutables
-    ];
-
-  mkDerivationOverrides = finalAttrs: oldAttrs: {
-
-    version = oldAttrs.version + "-git-${lib.strings.substring 0 7 oldAttrs.src.rev}";
-
-    meta = oldAttrs.meta // {
-      homepage = "https://codeberg.org/roberth/changelog-d";
-      maintainers = [ lib.maintainers.roberth ];
-    };
-
-  };
-in
-  (haskellModifications hsPkg).overrideAttrs mkDerivationOverrides