Export metrics in graphite format

[tulinkry]

OpenGrok 1.4.5 exposes metrics in prometheus format. It would be nice to have it in graphite format too if it's possible.

[vladak]

Given that most of the meters are constructed using builder it would be possible to return list of MeterRegistry objects from Metrics and change the builders to use forEach to do the register(). An alternative would be to build a facade in Metrics and make sure all meters are built/registered using that.