[9.1](backport #45093) otel: allow filebeat otel to load otel config files

[mergify]

Proposed commit message

Currently the filebeat otel command only loads beats config files, which it then translates to beats receivers in order to run a OTel collector.

This PR augments this functionality to allow the command to load otel configuration files, this aids in testing and running beats receivers in a standalone collector without depending on EDOT.

How to test

cd x-pack/filebeat/
go test -c -tags otelbeat
mage docker:composeUp
go test   -tags "integration" -run 'TestFilebeatOTel.*' ./tests/integration -v -count=1

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.

Related

• Relates [beatreceiver] Add otel test framework #44705

  ---

  This is an automatic backport of pull request otel: allow filebeat otel to load otel config files #45093 done by Mergify.

[mergify]

Cherry-pick of 46e855e has failed:

On branch mergify/bp/9.1/pr-45093
Your branch is up to date with 'origin/9.1'.

You are currently cherry-picking commit 46e855e22.
  (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:   libbeat/otelbeat/beatconverter/beatconverter.go
	modified:   x-pack/filebeat/tests/integration/otel_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   NOTICE.txt
	both modified:   go.mod
	both modified:   x-pack/libbeat/common/otelbeat/otel.go

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/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mergify]

This pull request has not been merged yet. Could you please review and merge it @mauri870? 🙏

[mergify]

This pull request has not been merged yet. Could you please review and merge it @mauri870? 🙏