fixup(buildClan): split up the inner-module into: {forSystem, forName}

I am preparing this such that we can move the forName modules into the
defaults for the deferred module outputs and the forSystem modules are
added later and only for the 'configsPerSystem' where we actually need
the system modules

lib/build-clan/machineModules/forName.nix

@@ -0,0 +1,28 @@
+{
+  name,
+  directory,
+}:
+{
+  _class,
+  lib,
+  ...
+}:
+{
+  imports = [
+    {
+      imports = builtins.filter builtins.pathExists (
+        [
+          "${directory}/machines/${name}/configuration.nix"
+        ]
+        ++ lib.optionals (_class == "nixos") [
+          "${directory}/machines/${name}/hardware-configuration.nix"
+          "${directory}/machines/${name}/disko.nix"
+        ]
+      );
+    }
+    # TODO: move into nixos modules
+    ({
+      networking.hostName = lib.mkDefault name;
+    })
+  ];
+}

lib/build-clan/machineModules/forSystem.nix

@@ -0,0 +1,26 @@
+{
+  pkgs,
+  pkgsForSystem,
+  system,
+}:
+{
+  lib,
+  ...
+}:
+{
+  imports = [
+    (
+      {
+        # For vars we need to override the system so we run vars
+        # generators on the machine that runs `clan vars generate`. If a
+        # users is using the `pkgsForSystem`, we don't set
+        # nixpkgs.hostPlatform it would conflict with the `nixpkgs.pkgs`
+        # option.
+        nixpkgs.hostPlatform = lib.mkIf (system != null && (pkgsForSystem system) != null) (
+          lib.mkForce system
+        );
+      }
+      // lib.optionalAttrs (pkgs != null) { nixpkgs.pkgs = lib.mkForce pkgs; }
+    )
+  ];
+}