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.

.yo-rc.json

@@ -0,0 +1,12 @@
+{
+  "@microsoft/generator-sharepoint": {
+    "version": "1.4.1",
+    "libraryName": "expiry-indicator",
+    "libraryId": "68bb6d2d-9895-45b4-88e8-b98835faa981",
+    "environment": "onprem",
+    "packageManager": "npm",
+    "solutionName": "expiry-indicator",
+    "componentType": "extension"
+  }
+}
+