Image building take 2

We want verity protected partitions as well as encrypted state/data along with verified boot.
This PR integrates Peter Marshall's awesome little Nixlet project as a starting point, especially the nice testing scaffolding will be super helpful! ✨

https://github.com/petm5/nixlet/

modules/config/minimal-modules.nix

@@ -0,0 +1,15 @@
+{ config, ... }:
+{
+  boot = {
+    bootspec.enable = false;
+    initrd.kernelModules = config.boot.kernelModules;
+    kernel.enable = false; # No kernel or modules in the rootfs
+    modprobeConfig.enable = false;
+  };
+
+  system.build = {
+    inherit (config.boot.kernelPackages) kernel;
+  };
+
+  system.modulesTree = [ config.boot.kernelPackages.kernel ] ++ config.boot.extraModulePackages;
+}

modules/config/minimal-system.nix

@@ -0,0 +1,26 @@
+{ ... }:
+{
+
+  nixpkgs.overlays = [
+    (final: prev: {
+
+      composefs = final.callPackage ../../pkgs/composefs.nix { inherit prev; };
+      qemu_tiny = final.callPackage ../../pkgs/qemu.nix { inherit prev; };
+      systemdUkify = final.callPackage ../../pkgs/systemd-ukify.nix { inherit prev; };
+
+    # # FIXME: Revisit + refine these below in a future image minimization effort
+    #
+    # util-linux = prev.util-linux.override {
+    #   ncursesSupport = false;
+    #   nlsSupport = false;
+    # };
+    #
+    # dbus = prev.dbus.override {
+    #   enableSystemd = false;
+    #   x11Support = false;
+    # };
+
+    })
+  ];
+
+}