Migrate the elasticsearch output to go-elasticsearch

[faec]

What does this PR do?

Migrate the Elasticsearch output from the old custom client library in libbeat to the official go-elasticsearch client.

Closes #14.

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.md or CHANGELOG-developer.md.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @faec? 🙏.
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: 2022-11-30T18:53:48.441+0000

• Duration: 15 min 18 sec

❕ Flaky test report

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🤖 GitHub comments

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[leehinman]

I really like how this is simplifying things.

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b esclient upstream/esclient
git merge upstream/main
git push upstream esclient

[cmacknz]

I really like how this is simplifying things.

Agree, took a quick look and this is looking good. Thanks @faec!

To one of Lee's points, let's make sure we have all the follow up work accurately captured into issues so we have a good view of what work is left. There was a preliminary list tracked under "Implement an Elasticsearch output" on #16 that may now be out of date.

One issue we may want to follow is elastic/go-elasticsearch#557. We aren't at the point of performance testing yet where this would come up, but we'll get there eventually.