[elasticsearch] support api_key

[klacabane]

Summary

Adds support for api_key authentication in the elasticsearch module

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.

How to test this PR locally

• create an api key and grab the beats format[1]
• configure elasticsearch module to use that api_key:

metricbeat.modules:
  - module: elasticsearch
    xpack.enabled: true
    hosts: ["http://localhost:9200"]
    api_key: <key in beats format>
    period: 10s

• elasticsearch metricsets are successfully collecting documents

[1]

Related issues

• Closes [Stack Monitoring] Add missing metricbeat api_key configuration to elasticsearch integration module integrations#4949

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 @klacabane? 🙏.
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]

💚 Build Succeeded

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Build stats

• Start Time: 2023-08-11T13:50:27.417+0000

• Duration: 56 min 1 sec

Test stats 🧪

Test	Results
Failed	0
Passed	4464
Skipped	913
Total	5377

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

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To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages and run the E2E tests.

• /beats-tester : Run the installation tests with beats-tester.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[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 4949-es-api-key upstream/4949-es-api-key
git merge upstream/main
git push upstream 4949-es-api-key

[mohamedhamed-ahmed]

LGTM!