feat(pipeline): balanced splits

[lemeurherve]

This change implements balanced splits using splitTests from parallel executor plugin extracting splits from junit records of the previous build, to efficiently pack all combinations of repositories and their plugin(s) to get similar pct tests durations across all splits.

In case we can't use splitTests results (first build, or tests not executed previously ex: weekly-test label then full-test one), it extracts splits from stored bom reports (#7297).

For new repositories that were not in previous junit records or stored bom reports, it will use the previous method from #7256 to distribute them in additional fixed splits.

For the beginning stored bom reports can be updated manually, a future improvement could be to open a pull request on reports when running from master. (Out of scope for the implementation of balanced splits)

With this change, I observed in my builds that run pct stage take about 35~45mins, versus currently 1h~1h10mins with fixed splits.

Ref:

• Decrease BOM costs #7073
• Decrease BOM costs by splitting tests more efficiently jenkins-infra/helpdesk#5208

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed