feat(server): custom library scanning interval (#4390)

* add automatic library scan config options

* add validation

* open api

* use CronJob instead of cron-validator

* fix tests

* catch potential error of the library scan initialization

* better description for input field

* move library scan job initialization to server app service

* fix tests

* add comments to all parameters of cronjob contructor

* make scan a child of a more general library object

* open api

* chore: cleanup

* move cronjob handling to job repoistory

* web: select for common cron expressions

* fix open api

* fix tests

* put scanning settings in nested accordion

* fix system config validation

* refactor, tests

---------

Co-authored-by: Jason Rasmussen <jrasm91@gmail.com>

mobile/openapi/test/system_config_library_scan_dto_test.dart

@@ -0,0 +1,32 @@
+//
+// AUTO-GENERATED FILE, DO NOT MODIFY!
+//
+// @dart=2.12
+
+// ignore_for_file: unused_element, unused_import
+// ignore_for_file: always_put_required_named_parameters_first
+// ignore_for_file: constant_identifier_names
+// ignore_for_file: lines_longer_than_80_chars
+
+import 'package:openapi/api.dart';
+import 'package:test/test.dart';
+
+// tests for SystemConfigLibraryScanDto
+void main() {
+  // final instance = SystemConfigLibraryScanDto();
+
+  group('test SystemConfigLibraryScanDto', () {
+    // String cronExpression
+    test('to test the property `cronExpression`', () async {
+      // TODO
+    });
+
+    // bool enabled
+    test('to test the property `enabled`', () async {
+      // TODO
+    });
+
+
+  });
+
+}