Add Current Navigation Application Customizer

- Created a new SPFx Application Customizer for current navigation.
- Implemented core functionality to fetch and render navigation items from a SharePoint term set.
- Added styles for the navigation component using SCSS.
- Included localization support for English and German languages.
- Developed unit tests for core navigation functionalities.
- Configured TypeScript and TSLint settings for the project.
- Added validation scripts for static assets and package configuration.

src/extensions/currentNavigation/loc/de-de.js

@@ -0,0 +1,8 @@
+define([], function() {
+  return {
+    "Title": "CurrentNavigationApplicationCustomizer",
+    "NavigationLabel": "Navigation der aktuellen Website",
+    "ConfigurationMissing": "Die aktuelle Navigation ist nicht konfiguriert.",
+    "LoadError": "Die aktuelle Navigation konnte nicht geladen werden."
+  };
+});