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.

package.json

@@ -0,0 +1,33 @@
+{
+  "name": "expiry-indicator",
+  "version": "1.0.0",
+  "private": true,
+  "engines": {
+    "node": ">=6.9.0 <9.0.0"
+  },
+  "scripts": {
+    "build": "gulp bundle",
+    "clean": "gulp clean",
+    "package-solution": "gulp package-solution",
+    "package": "gulp clean && gulp bundle --ship && gulp package-solution --ship",
+    "test": "gulp test"
+  },
+  "dependencies": {
+    "@microsoft/sp-core-library": "1.4.1",
+    "@microsoft/sp-dialog": "1.4.1",
+    "@microsoft/sp-http": "1.4.1",
+    "@microsoft/sp-listview-extensibility": "1.4.1",
+    "@types/es6-promise": "0.0.33",
+    "@types/webpack-env": "1.13.1"
+  },
+  "devDependencies": {
+    "@microsoft/sp-build-web": "1.4.1",
+    "@microsoft/sp-module-interfaces": "1.4.1",
+    "@microsoft/sp-tslint-rules": "1.4.1",
+    "@types/chai": "3.4.34",
+    "@types/mocha": "2.2.38",
+    "ajv": "5.2.2",
+    "gulp": "~3.9.1"
+  }
+}
+