proposal: testing: testing.Benchmark: Allow for other aggregations other than average

[YesYouKenSpace]

Proposal Details

Goal: allow for metrics to be collected and output in choice of aggregations such as (max, min, percentiles)

[seankhliao]

I believe that's what https://pkg.go.dev/testing#B.ReportMetric is for
though in general, the overhead of calculation for other stats will likely be too high to be feasible to do accurately.