EngineStateMonitor#TIMER instance not created with daemon thread

[ibragfir]

Description

As part of our build, we're starting our spring-boot app (which starts InMemoryEngine), running all of our tests and then stopping the app with spring-boot-maven-plugin. However, our doesn't gracefully finish due to a WAITING non-daemon thread.

Analyzing the code, we've identified that it's the EngineStateMonitor#TIMER instance is created with default Timer() constructor which starts the TimerThread as non-daemon.
We do shutdown the engine ZeebeTestEngine#stop and a client ZeebeClient#close.

Expected behaviour

TIMER instance needs to be created with a daemon thread TIMER = new Timer(true) so that the app shuts down gracefully.
Or make sure stopping the test engine also stops the TIMER instance and frees up the resources.

[remcowesterhoud]

Thanks for raising and analyzing @ibragfir! I agree it makes sense to run the Timer as a daemon. Would you mind creating a PR for this?