systemd-bootchart: init at 235

Add the systemd-bootchart package. At this stage just adding the
package. The plan is to add the module and kernel configurations for the
boot invocation in a follow up PR.

Being utilized in nixosConfigurations as part of Ghaf, where the
systemd-analyze does not provide enough information, especially cpu and
mem usages for throttling the start of some of the virtual machines.

This has been tested locally in realtime with:

```
/nix/store/...-systemd-bootchart-235/lib/systemd/systemd-bootchart --rel -o $(mktemp -d)
```

Waiting the requisite 20 seconds and then viewing the created .svg file.

Signed-off-by: Brian McGillion <bmg.avoin@gmail.com>

pkgs/by-name/sy/systemd-bootchart/package.nix

@@ -0,0 +1,49 @@
+{
+  lib,
+  stdenv,
+  fetchFromGitHub,
+  autoreconfHook,
+  pkg-config,
+  systemd,
+  libxslt,
+  docbook_xsl,
+  docbook_xml_dtd_45,
+}:
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "systemd-bootchart";
+  version = "235";
+
+  src = fetchFromGitHub {
+    owner = "systemd";
+    repo = "systemd-bootchart";
+    tag = "v${finalAttrs.version}";
+    hash = "sha256-1h6/Q6ShfJbu/DXENIe5GAQiZp4jlOAg6SAR36cmg2I=";
+  };
+
+  strictDeps = true;
+
+  nativeBuildInputs = [
+    autoreconfHook
+    pkg-config
+    libxslt
+    docbook_xsl
+    docbook_xml_dtd_45
+  ];
+
+  buildInputs = [
+    systemd
+  ];
+
+  configureFlags = [
+    "--with-rootprefix=$(out)"
+  ];
+
+  meta = {
+    description = "Boot performance graphing tool from systemd";
+    homepage = "https://github.com/systemd/systemd-bootchart";
+    license = lib.licenses.lgpl21Plus;
+    maintainers = [ lib.maintainers.brianmcgillion ];
+    platforms = lib.platforms.linux;
+  };
+})