Add --web.disable-exporter-metrics

[candlerb]

ipmi_exporter returns a bunch of go internal metrics:

curl localhost:9290/metrics
# HELP go_gc_duration_seconds A summary of the GC invocation durations.
# TYPE go_gc_duration_seconds summary
go_gc_duration_seconds{quantile="0"} 0
go_gc_duration_seconds{quantile="0.25"} 0
go_gc_duration_seconds{quantile="0.5"} 0
go_gc_duration_seconds{quantile="0.75"} 0
go_gc_duration_seconds{quantile="1"} 0
go_gc_duration_seconds_sum 0
go_gc_duration_seconds_count 0
# HELP go_goroutines Number of goroutines that currently exist.
# TYPE go_goroutines gauge
go_goroutines 9
... etc

It would be nice to have a flag to disable these, as node_exporter has:

                disableExporterMetrics = kingpin.Flag(
                        "web.disable-exporter-metrics",
                        "Exclude metrics about the exporter itself (promhttp_*, process_*, go_*).",
                ).Bool()
...

Otherwise these metrics need to be filtered out by metric relabelling.

[bitfehler]

Hi! The linked node exporter PR doesn't look trivial at first glance, I will need some time to look at this. Since the metrics can be filtered out by relabeling I wouldn't consider this a pressing issue. Valid nonetheless, thanks for reporting.