fix: cleanup metrics state management in runner

[jakobmoellerdev]

This properly deregisters and registers metrics based on the runner of the metrics exporter. This allows to stop the manager runnable and start it at a later time again (e.g. for in-process restarting). This will not affect existing behavior and just allows proper restarting.

All Unregister limitations apply:

Note that even after unregistering, it will not be possible to register a new Collector that is inconsistent with the unregistered Collector, e.g. a Collector collecting metrics with the same name but a different help string. The rationale here is that the same registry instance must only collect consistent metrics throughout its lifetime

[llamerada-jp]

Is this change to address memory (or some resources) leaks? If so, I think I have to change other products (like pvc-autoresizer). I would be grateful if you could tell me.

[jakobmoellerdev]

@llamerada-jp no leak potential the only thing that won't work is restarting the affected runner in process (any case where Register is called twice before calling Unregister). No other side effects AFAIK.