[9.1](backport #45314) otel: update filebeat integration tests to run in isolation

[mergify]

Proposed commit message

As a leftover from #45093, the tests added reuse the index names which may cause issues when running the tests in sequence without cleaning up first. Additionally, the beats receivers should not use the same path.home.

Adjusted the existing tests to use unique indexes and individual home folders.

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 issues

• Relates otel: allow filebeat otel to load otel config files #45093
• Relates otel: add otel-specific fields to ingested docs #45242

---

This is an automatic backport of pull request #45314 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of ea98564 has failed:

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	both modified:   x-pack/filebeat/tests/integration/otel_test.go

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[github-actions]

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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? 🙏

[mauri870]

This backport depends on #45324, and that backport is failing consistently on 9.1/9.0. I have to investigate why that is the case.

[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? 🙏

[mauri870]

Closing for now, see rationale in #45324.