Create `goBackwardCompatibleMetrics` option that defaults to true

As I was fixing #224 I've noticed that for Go benchmarks that output multiple metrics the action prior to `v1.18.0` was extracting a unit that was slightly wrong. For this reason to keep backward compatibility I've kept this metric (PR #225) being calculated like that (in addition to the new way with multiple metric)

We should create an option that would default to keep this backward compatibility but would enable opting out of this behavior. In the next version it would get deprecated with a warning and then removed with only one way of extracting metrics