Add Elastic-Agent event log documentation

[belimawr]

This PR adds documentation for the feature introduced by elastic/elastic-agent#4549

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[mergify]

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

• backport-/d./d is the label to automatically backport to the /d./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[kilfoyle]

LGTM! Thanks @belimawr!

[belimawr]

I'll wait until elastic/elastic-agent#4549 is merged to merge this PR.

[kilfoyle]

LGTM! Thanks for adding this @belimawr!

By the way, kind of related to logging, if you have a chance I'd appreciate a review of this PR. It's kind of old now. Sorry I lost track of it. :-)

[belimawr]

By the way, kind of related to logging, if you have a chance I'd appreciate a review of this PR. It's kind of old now. Sorry I lost track of it. :-)

Approved!

[jlind23]

@belimawr can we get this merged? :-)

[belimawr]

I'm waiting for the PR with the feature elastic/elastic-agent#4549, to be merged before merging this one.

[jlind23]

elastic/elastic-agent#4549 has been merged hence merging this one.