functionaltests: wait for aggregation data steams

[endorama]

Motivation/summary

Today's functional-tests run failed due to executing the first data stream check before all data stream we expect to be present were there.
This may happen due to the 1m aggregation data streams being not yet created if the data stream check happens too fast.
Ideally this problem was fixed with the initial implementation, but it only reduced its occurrence.
This PR introduces an additional check in RunBlocking to verify if other dta strea'ms are present, ignoring the document count (which is problematic for aggregation data streams).

Checklist

How to test these changes

https://github.com/elastic/apm-server/actions/runs/12892900589

Related issues

#14100

[mergify]

This pull request does not have a backport label. Could you fix it @endorama? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label.

[endorama]

We decided to take a different approach than what is in this PR. This approach has been implemented in #15356.

I'm closing this PR as superseded by the other one. Thanks @kruskall for the review 🚀