Dynamic logger ecs reconfig

[eyalkoren]

What does this PR do?

Checklist

• 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
  • I have made corresponding changes to the documentation
• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix
• This is a new plugin
  • I have updated CHANGELOG.asciidoc
  • My code follows the style guidelines of this project
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • New and existing unit tests pass locally with my changes
  • I have updated supported-technologies.asciidoc
  • I have added information to the Log correlation documentation
  • Added an API method or config option? Document in which version this will be introduced
  • Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• This is something else
  • I have updated CHANGELOG.asciidoc

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• Build Cause: Started by user eyalkoren

• Start Time: 2021-03-17T17:55:36.993+0000

• Duration: 50 min 19 sec

• Commit: d4622aa

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Total	1898

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[felixbarny]

I know this is not ready yet but I was too curious about this PR :)

[eyalkoren]

OK, at last ready for a review. Supported technologies page is updated with supported versions (and the addition of Logback). Legacy tests use the earliest-supported version and there is a test for a recent version. For log4j1, the earliest supported version is the latest version, as it is the first compiled with Java 1.4.

Also worth noticing: the ECS service.name field is set with what should be the most relevant service name, meaning with preference to the the service name of the current active span, if there is such, otherwise the configured service name. Assuming that logs are not ingested not through APM, this should allow the best correlation between log events and APM event.

[felixbarny]

We might have to refine how the service.name is computed but let's not block this PR on that. It's an experimental feature anyway.