Feature/configurable topn count

[leoparente]

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[leoparente]

@rboucher-ns1 i did it per policy at same level of deep sample and periods should it be at each handler level?
@weyrick what are your thoughts?

[rboucher-me]

The ideal scenario would be to set it at the individual metric level in the handler configuration (dns_top_qnames3_items=20). Second-best would be at the handler level (top_items=20).
That said, I think setting this at the policy level is sufficient. The purpose of this is to allow us to do some testing and tuning (particularly for flow metrics) to find the ideal compromise between data granularity and compute/storage requirements.