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.

src/extensions/expiryIndicator/ExpiryIndicatorFieldCustomizer.manifest.json

@@ -0,0 +1,10 @@
+{
+  "$schema": "https://developer.microsoft.com/json-schemas/spfx/client-side-extension-manifest.schema.json",
+  "id": "a555f4fc-d6a6-4421-8189-457449d9bbde",
+  "alias": "ExpiryIndicatorFieldCustomizer",
+  "componentType": "Extension",
+  "extensionType": "FieldCustomizer",
+  "version": "1.0.0",
+  "manifestVersion": 2
+}
+