[prometheus-metrics-ghc] Invalid metric ghc_gcdetails_gen

[jfraudeau]

ghc_gcdetails_gen is exported as a histogram but it's data doesn't conform to that of a histogram which would consist of a count of values in different buckets. The count being exposed a the metric value and the bucket defined as a le label.

I don't know if it would make more sense to disable the metric or to conform it to a proper histogram. Making it a proper histogram would require the introduction of a state to keep track of all occurrences between collections and differs from the current design of prometheus-metrics-ghc.

https://github.com/fimad/prometheus-haskell/blob/9d38241cce4a4318cd999928801eaf7bcd747633/prometheus-metrics-ghc/src/Prometheus/Metric/GHC.hs#L262-L269