Make SystemMetricsProducer more configurable

[rc-mairovichaa]

Now it's all or nothing in terms of MetricsProducer choice. It's suggested to add possibility to override particular MetricsProducer (for example, to provide client's version of GarbageCollectorsMetricsProducer without overriding all other producers as well as logic of their creation encapsulated in SystemMetricsProducer.