Add Expiry Indicator functionality with configuration and command set

- Implemented ExpiryItemService to manage expiry date logic for list items.
- Created ExpiryModels to define types and structures for expiry configurations and rules.
- Added RestError utility for handling API response errors.
- Developed ExpiryIndicatorFieldCustomizer to display expiry information in list views.
- Introduced ExpiryIndicatorCommandSet for extending expiry dates and managing settings.
- Added settings dialog for configuring expiry settings.
- Implemented localization support for English and German languages.
- Added TypeScript configuration files for project setup.
- Included TSLint configuration for code quality enforcement.

config/package-solution.json

@@ -0,0 +1,27 @@
+{
+  "$schema": "https://developer.microsoft.com/json-schemas/spfx-build/package-solution.schema.json",
+  "solution": {
+    "name": "expiry-indicator-client-side-solution",
+    "id": "68bb6d2d-9895-45b4-88e8-b98835faa981",
+    "version": "1.0.0.0",
+    "includeClientSideAssets": true,
+    "skipFeatureDeployment": false,
+    "features": [
+      {
+        "title": "ExpiryIndicator command set registration",
+        "description": "Registers ExpiryIndicator commands for modern lists and document libraries. Does not provision ExpiryDate.",
+        "id": "913402af-ab9a-4974-9f86-5c2159ae41db",
+        "version": "1.0.0.0",
+        "assets": {
+          "elementManifests": [
+            "elements.xml"
+          ]
+        }
+      }
+    ]
+  },
+  "paths": {
+    "zippedPackage": "solution/expiry-indicator.sppkg"
+  }
+}
+