clan tests: allow testing CLI interactions

This is an improvement of the clanTest nixos vm test module.

The module now has a new option clan.test.fromFlake that allows to specify a flake.nix as the source for the test clan instead of specifying clan.XXX options.

This in turn allows accessing the `flake.nix` inside the test driver allowing to use the clan cli on it

checks/dummy-inventory-test-from-flake/legacy-module/README.md

@@ -0,0 +1,10 @@
+---
+description = "Set up dummy-module"
+categories = ["System"]
+features = [ "inventory" ]
+
+[constraints]
+roles.admin.min = 1
+roles.admin.max = 1
+---
+

checks/dummy-inventory-test-from-flake/legacy-module/roles/admin.nix

@@ -0,0 +1,5 @@
+{
+  imports = [
+    ../shared.nix
+  ];
+}

checks/dummy-inventory-test-from-flake/legacy-module/roles/peer.nix

@@ -0,0 +1,5 @@
+{
+  imports = [
+    ../shared.nix
+  ];
+}

checks/dummy-inventory-test-from-flake/legacy-module/shared.nix

@@ -0,0 +1,34 @@
+{ config, ... }:
+{
+  systemd.services.dummy-service = {
+    enable = true;
+    description = "Dummy service";
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      Type = "oneshot";
+      RemainAfterExit = true;
+    };
+    script = ''
+      generated_password_path="${config.clan.core.vars.generators.dummy-generator.files.generated-password.path}"
+      if [ ! -f "$generated_password_path" ]; then
+        echo "Generated password file not found: $generated_password_path"
+        exit 1
+      fi
+      host_id_path="${config.clan.core.vars.generators.dummy-generator.files.host-id.path}"
+      if [ ! -e "$host_id_path" ]; then
+        echo "Host ID file not found: $host_id_path"
+        exit 1
+      fi
+    '';
+  };
+
+  # TODO: add and prompt and make it work in the test framework
+  clan.core.vars.generators.dummy-generator = {
+    files.host-id.secret = false;
+    files.generated-password.secret = true;
+    script = ''
+      echo $RANDOM > "$out"/host-id
+      echo $RANDOM > "$out"/generated-password
+    '';
+  };
+}