Introduce new CustomEvent for InventoryPlugin signaling that initial DB processing at JobScheduler start is finished

Current Situation
If a JobScheduler is not started and JobScheduler Objects are added, renamed or deleted on the filesystem the JOC Cockpit does not know about these changes.
When the JobScheduler starts the initial Inventory update of the database entries does not send any custom events, therefore such changes are not reflected in JOC Cockpit if the corresponding view is opened currently.

Desired Behavior

1. To make the JOC Cockpit aware of the changes, the initial inventory update should send a custom event InventoryInitialized to signal that the initial database update is finished.
   • This event has no relation to specific JobScheduler objects and therefore does not have a path attribute.
2. The webservice for the /events URI has to process the new custom event InventoryInitialized.
3. The JOC Cockpit GUI has also to process the event InventoryInitialized sent by the /events URI.