chore(server): Store generated files (thumbnails, encoded video) in subdirectories (#4112)

* save thumbnails in subdirectories

* migration job, migrate assets and face thumbnails

* fix tests

* directory depth of two instead of three

* cleanup empty dirs after migration

* clean up empty dirs after migration, migrate people without assetId

* add job card for new migration job

* fix removeEmptyDirs race condition because of missing await

* cleanup empty directories after asset deletion

* move ensurePath to storage core

* rename jobs

* remove unnecessary property of IEntityJob

* use updated person getById, minor refactoring

* ensure that directory cleanup doesn't interfere with migration

* better description for job in ui

* fix remove directories when migration is done

* cleanup empty folders at start of migration

* fix: actually persist concurrency setting

* add comment explaining regex

* chore: cleanup

---------

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

mobile/openapi/test/system_config_job_dto_test.dart

@@ -36,6 +36,11 @@ void main() {
       // TODO
     });
 
+    // JobSettingsDto migration
+    test('to test the property `migration`', () async {
+      // TODO
+    });
+
     // JobSettingsDto objectTagging
     test('to test the property `objectTagging`', () async {
       // TODO