parse container ID with cgroups v2

[SylvainJuge]

What does this PR do?

Implements container ID parsing for cgroups v2.

Closes #3035
Replaces #2352 (it was simpler to start a fresh one due to refactoring, but the heuristic is similar)

Checklist

• open spec PR on https://github.com/elastic/apm for spec + shared agents testing: Modify spec for cgroups v2 container ID parsing apm#807
• This is an enhancement of existing features, or a new feature in existing plugins
  • I have updated CHANGELOG.asciidoc
  • I have added tests that prove my fix is effective or that my feature works
  • Added an API method or config option? Document in which version this will be introduced n/a
  • I have made corresponding changes to the documentation n/a

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• Start Time: 2023-07-03T11:39:14.976+0000

• Duration: 14 min 47 sec

❕ Flaky test report

No test was executed to be analysed.

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