k6: group special async function treatment

[mstoykov]

A group provided with an async function will now:

1. Treat the whole time it take for the async function promise to finisher the duration of the group.
2. It will also use goja's AsyncContextTracker to make it so that the code using await within the group will still continue to be tagged with the group after await returns.
3. Instead of directly calling the async function it schedules it to be called the next time a promise job will work.

The current AsyncContextTracker is only used for this and as such is directly changed in the k6 module. In the future there likely will be API so that multiple modules can use it simultaneously, but that seems way too involved to be included in this change and also currently only group needs this.

fixes #2848 #2728

[mstoykov]

Moving this to a draft in favor of https://github.com/grafana/k6/pull/2875

[aakash3771]

How to get notified when this is fixed?

[mstoykov]

For more information you likely should follow https://github.com/grafana/k6/issues/2728 as this PR at this time is very unlikely to be merged as is.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 86.56716% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 76.15%. Comparing base (0b563d4) to head (8101130). Report is 594 commits behind head on master.

Files	Patch %	Lines
js/modules/k6/k6.go	83.33%	4 Missing and 1 partial :warning:
js/modules/k6/asyncGroup.go	89.18%	2 Missing and 2 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2863      +/-   ##
==========================================
- Coverage   76.15%   76.15%   -0.01%     
==========================================
  Files         217      218       +1     
  Lines       16604    16669      +65     
==========================================
+ Hits        12645    12694      +49     
- Misses       3185     3196      +11     
- Partials      774      779       +5     

Flag	Coverage Δ
ubuntu	75.97% <86.56%> (-0.01%)	:arrow_down:
windows	75.85% <86.56%> (+<0.01%)	:arrow_up:

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[mstoykov]

I am closing this PR as it is really unlikely we will go down this route