Allow users to define their own metrics and don't force using correctness

[davidberenstein1957]

w.r.t. the correctness, I think internally there are some niche methods that would need to be overhauled too.

like report.correctness_by_topic()

instead we could do something like metrics_by_topic("correctness") or something

[GTimothee]

So the idea would be to remove the computation of correctness by default, and therefore change the report so that it only displays what it can, right ? Because so far I think the report always try to show correctness by components.

[davidberenstein1957]

Because

Yes. I think we can see if we could open this up easily; if not, we can leave it for a more serious refactor and perhaps focus on another issue. I have not looked at the current setup. Still, ideally, we want it to be backwards compatible and don't want to make major/breaking changes, which might be especially difficult in the report generation.