Document ES output API usage

[belimawr]

Proposed commit message

This commit documents the _bulk API usage by the Elasticsearch output and how different status codes are handled.

Checklist

- [ ] My code follows the style guidelines of this project
- [ ] I have commented my code, particularly in hard-to-understand areas

• I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
  - [ ] I have added tests that prove my fix is effective or that my feature works
  - [ ] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

## Author's Checklist

How to test this PR locally

Assuming beats and docs are both in $GIT_HOME, build the docs:

$GIT_HOME/docs/build_docs --respect_edit_url_overrides --doc $GIT_HOME/beats/filebeat/docs/index.asciidoc --resource=$GIT_HOME/beats/x-pack/filebeat/docs --chunk 1 --open

A browser window will open, then navigate to the Elasticsearch output documentation and scroll until the end of the page

Related issues

• Closes Do not consider 409 Conflict responses from _bulk an error when ingesting to data streams #36547

## Use cases
## Screenshots
## Logs

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @belimawr? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

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• Start Time: 2023-10-24T13:55:50.568+0000

• Duration: 9 min 36 sec

❕ Flaky test report

No test was executed to be analysed.

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