[RFE] pmrep support for listing metrics in a metricset

[myllynen]

When e.g. working with large archives it can be helpful to create first a smaller archive covering only a certain timeframe with only the relevant metrics needed for further investigation. In case of pmrep, it provides several helpful metricsets for diagnosing issues but when creating these kind of smaller archives with pmlogextract it is time-consuming to manually check what are all the metrics needed for a metricset.

A special option which would simply just print the non-derived metrics needed by pmrep to report a metricset would help in this case. Certainly a nice-to-have feature but perhaps worth considering and adding. Thanks.