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/serve.json

@@ -0,0 +1,26 @@
+{
+  "$schema": "https://developer.microsoft.com/json-schemas/spfx-build/spfx-serve.schema.json",
+  "port": 4321,
+  "https": true,
+  "serveConfigurations": {
+    "fieldCustomizer": {
+      "pageUrl": "https://sharepoint/sites/demo/Lists/Test/AllItems.aspx",
+      "fieldCustomizers": {
+        "ExpiryDate": {
+          "id": "a555f4fc-d6a6-4421-8189-457449d9bbde",
+          "properties": {}
+        }
+      }
+    },
+    "commandSet": {
+      "pageUrl": "https://sharepoint/sites/demo/Lists/Test/AllItems.aspx",
+      "customActions": {
+        "cd58f5d9-ffc8-4df7-a910-3054842d7abf": {
+          "location": "ClientSideExtension.ListViewCommandSet.CommandBar",
+          "properties": {}
+        }
+      }
+    }
+  }
+}
+