add monitoring

config/health/resources/AppKey.yml

@@ -0,0 +1,11 @@
+name: App Key
+abbreviation: appkey
+checker: PragmaRX\Health\Checkers\Expression
+notify: true
+column_size: 3
+error_message: "There is no app key defined"
+graph_enabled: false
+targets:
+- default:
+    expression_value: "config('app.key') !== null"
+    should_return: true