[9.1](backport #45359) x-pack/filebeat/input/cel: add support for token authentication

[mergify]

Proposed commit message

See title.

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• 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.

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---

This is an automatic backport of pull request #45359 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 5c91c96 has failed:

On branch mergify/bp/9.1/pr-45359
Your branch is up to date with 'origin/9.1'.

You are currently cherry-picking commit 5c91c960d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   x-pack/filebeat/input/cel/config_auth.go
	modified:   x-pack/filebeat/input/cel/input.go
	modified:   x-pack/filebeat/input/cel/input_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   docs/reference/filebeat/filebeat-input-cel.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[elasticmachine]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

[github-actions]

🔍 Preview links for changed docs

• docs/reference/filebeat/filebeat-input-cel.md