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_dto_test.dart

@@ -26,6 +26,11 @@ void main() {
       // TODO
     });
 
+    // SystemConfigLibraryDto library_
+    test('to test the property `library_`', () async {
+      // TODO
+    });
+
     // SystemConfigMachineLearningDto machineLearning
     test('to test the property `machineLearning`', () async {
       // TODO