Add explicit composer.json.

Closes #3481974

composer.json

+{
+  "name": "drupal/navigation_extra_tools",
+  "description": "Provide useful tools to Drupal Navigation.",
+  "type": "drupal-module",
+  "license": "GPL-2.0-or-later",
+  "require": {
+      "php": ">=8.1"
+  },
+  "homepage": "https://www.drupal.org/project/navigation_extra_tools",
+  "authors": [
+      {
+          "name": "James Shields",
+          "homepage": "https://www.drupal.org/u/lostcarpark",
+          "role": "Maintainer"
+      }
+  ],
+  "support": {
+      "issues": "https://www.drupal.org/project/issues/navigation_extra_tools",
+      "source": "https://git.drupalcode.org/project/advent_calendar"
+  }
+}