Add Portal Settings Web Part with styles, localization, and tests

- Implemented the PortalSettings Web Part with a new manifest and TypeScript file.
- Created SCSS styles for the Web Part, defining various UI elements and responsive design.
- Added localization support for English and German languages.
- Developed tests for Provider Registry and static assets validation.
- Included PowerShell script for project validation.

src/webparts/portalSettings/PortalSettingsWebPart.manifest.json

@@ -0,0 +1,24 @@
+{
+  "$schema": "https://developer.microsoft.com/json-schemas/spfx/client-side-web-part-manifest.schema.json",
+  "id": "c41d05ec-0682-4af0-b807-649806ed56b3",
+  "alias": "PortalSettingsWebPart",
+  "componentType": "WebPart",
+  "version": "*",
+  "manifestVersion": 2,
+  "requiresCustomScript": false,
+  "preconfiguredEntries": [
+    {
+      "groupId": "5c03119e-3074-46fd-976b-c60198311f70",
+      "group": { "default": "Other" },
+      "title": { "default": "Portal Settings", "de-de": "Portal-Einstellungen" },
+      "description": {
+        "default": "Central administration for installed portal extensions.",
+        "de-de": "Zentrale Verwaltung installierter Portal-Erweiterungen."
+      },
+      "officeFabricIconFontName": "Settings",
+      "properties": {
+        "title": "Zentrale Verwaltung der Portal-Erweiterungen"
+      }
+    }
+  ]
+}