[9.1](backport #46112) Add host processor to Beat processor

[andrzej-stencel]

Proposed commit message

Add add_host_metadata processor to the OpenTelemetry Beat processor

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.
  • I didn't add a changelog entry as the processor is not ready for public use

How to test this PR locally

1. Include the processor in Elastic Agent by adding it to https://github.com/elastic/elastic-agent/blob/89e0e9a5b0ebb376773de813a1fd2c0b2f30e74a/internal/pkg/otel/components.go.
2. Build the Elastic Agent
3. Run the Agent with an OTel config that includes the Beat processor.

Example OTel config:

service:
  pipelines:
    logs:
      receivers:
        - filebeatreceiver
      processors:
        - beat
      exporters:
        - debug

receivers:
  filebeatreceiver:
    filebeat:
      inputs:
        - type: filestream
          paths:
            - /tmp/logs-1k.log
    processors:
      # Configure a processor to prevent enabling default processors
      - add_fields:
          fields:
            custom_field: "custom_value"
    output:
      otelconsumer:
    path.data: /tmp/0819/data
    path.logs: /tmp/0819/logs
    queue.mem:
      flush.timeout: 0

processors:
  beat:
    processors:
      - add_host_metadata:
          netinfo:
            enabled: false

exporters:
  debug:
    use_internal_logger: false
    verbosity: normal

---

This is a manual backport of pull request #46112 done by @andrzej-stencel

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