Timer job never unlocked after an exception

**Describe the bug**
please refer to https://github.com/flowable/flowable-engine/issues/2354

**Expected behavior**
I think there's still a possibility to have a lock, now UnlockTimerJobsCmd is run in the catch code block, but there is no chance to execute this code block when the app process is closed by exception.

**Additional context**
Need a thread "ResetExpiredTimerJobsRunnable" run on an independent Thread just like ResetExpiredJobsRunnable, the lock happens in any exception will be unlocked.