Add SharePoint element manifests for PortalSettings pages

- Created elements-v1.1.xml, elements-v2.xml, and elements.xml to define the PortalSettingsPage modules for different versions.
- Added upgrade actions for v1.1 and v2 to apply the respective element manifests.
- Ensured that the PortalSettings.aspx file is included in the SitePages library with appropriate settings.

config/package-solution.json

@@ -3,7 +3,7 @@
   "solution": {
     "name": "portal-settings-client-side-solution",
     "id": "1c98e32d-bb7b-43b7-9625-074d6e4ea286",
-    "version": "1.0.0.0",
+    "version": "2.0.0.0",
     "includeClientSideAssets": true,
     "skipFeatureDeployment": false,
     "features": [
@@ -11,13 +11,16 @@
         "title": "Portal Settings",
         "description": "Provisioniert die zentrale Settings-Seite fuer aktive Portal-Erweiterungen.",
         "id": "57bd9daf-48f9-49e2-aebd-11b15a0b5e93",
-        "version": "1.0.0.0",
+        "version": "2.0.0.0",
         "assets": {
           "elementManifests": [
-            "elements.xml"
+            "elements-v2.xml"
           ],
           "elementFiles": [
             "PortalSettings.aspx"
+          ],
+          "upgradeActions": [
+            "upgrade-actions-v2.xml"
           ]
         }
       }