Werk #14285: Fix frozen Microcore (Livestatus not responding) during config reloads

The reload of the Microcore core and it's helper processed could freeze when the core had notifications pending during reload. This was caused by a deadlock between the Notification helper and the Microcore. The Microcore was still alive but waiting to the notification helper to terminate while the notification helper waited for the Microcore.

From the user perspective this resulted in Livestatus not being responsive while the cmc.log showed a message like: still X unsent events, sending them now.

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