Unregister metrics based on conditions

[StephenOTT]

Certain conditions should trigger metrics to be unregistered:

start with Duration Tracking (Activity Instance and Process Instance):

1. As per a configuration, if a new process definition is deployed for a existing definition, the previous definition will be un-registered from the Prometheus collection of collectors. This is not always the needed function as there are scenarios where there may be multiple active definitions of the same process def key.

note: If you just restart the engine the metrics will self-resolve. But for "forever" on camunda engine instances, it is important to un-register collectors.