Use a histogram

[tcolgate]

A histogram would probably be a better fit for the gc stats, we could follow the Go client library

go_gc_duration_seconds_count
go_gc_duration_seconds_sum
go_gc_duration_seconds

They use a summary, but I think a couple of histograms for

nodejs_gc_duration_seconds
nodejs_gc_reclaim_bytes

might be good

thoughts?

[SimenB]

Yeah, that makes sense! Care to open a PR for it?