[9.2] (backport #11394) [otel config translate] allow hosts to be string not just slice

[mergify]

What does this PR do?

Allows the hosts part of the beat output to be a string instead of a slice.

This is to match the behavior of beats which allows this.

Why is it important?

This means that more hand written configuration will work "out of the box" with beat receivers.

Checklist

• I have read and understood the pull request guidelines of this project.
• 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/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

None.

How to test this PR locally

cd internal/pkg/otel/translate
go test -run TestToOtelConfig

Related issues

• Closes OTel manager failed: failed to generate otel config: error translating config for output: ... 'hosts' source data must be an array or slice, got string #11352

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

---

This is an automatic backport of pull request #11394 done by [Mergify](https://mergify.com).

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 1f1f66d

Failed CI Steps

• x86_64:sudo: container
• x86_64:sudo: container - platform-ingest-elastic-agent-debian-11-1762801856
• x86_64:sudo: container - platform-ingest-elastic-agent-debian-13-1762801856

cc @leehinman