server: add linode profile init

modules/nixos/server/profiles/linode/image.nix

@@ -0,0 +1,23 @@
+{
+  pkgs,
+  lib,
+  inputs,
+  config,
+  ...
+}: let
+  make-disk-image = import "${inputs.nixpkgs}/nixos/lib/make-disk-image.nix";
+in {
+  system.build.image = make-disk-image {
+    inherit lib pkgs config;
+    partitionTableType = "none";
+    name = "linode-image";
+    format = "raw";
+    # Linode requires the image to be gzip'd
+    # unzipped image cannot exceed 6gb
+    postVM = ''
+      ${pkgs.gzip}/bin/gzip -6 -c -- $diskImage > \
+      $out/nixos-image-${config.system.nixos.label}-${pkgs.stdenv.hostPlatform.system}.img.gz
+      rm $diskImage
+    '';
+  };
+}