show request average duration for each group on end of test summary

[MooseSaeed]

Feature Description

I believe it would make a lot of sense if we can see the average request duration for each group by end of test.

Currently, only the checks shows for each group, If k6 team can add average duration as well it would be perfect.

Suggested Solution (optional)

No response

Already existing or connected issues / PRs (optional)

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[na--]

Something like this can currently be manually done by setting bogus (or real) thresholds on the relevant sub-metrics, though it's not very well documented (grafana/k6-docs#205). We also have an open issue for creating an API to make it easier (#1321).

All of that said, I am not sure our users will always want k6 to start doing what you suggest automatically 🤔 With a lot of groups, it will start to have serious performance implications, and it may not even be what everyone desires, since it will make the end-of-test summary quite noisy and more over-crowded than it already is 🤔 So, explicitly exposing the groups the user is interested might be the better UX...

One implementation obstacle to either approach is that sub-metrics need to be defined in the init context, while group() calls happen in the VU context... So, the "simplest" manual solution would probably require some duplication in the user scripts 😞

Another problem with groups in general is that the "parent" groups don't actually contain the values from their "children" (#2309), though that probably can be solved independently by making threshold / sub-group definitions more flexible (#1313).