otel: trim non-otel configuration from when validating the otel configuration

[mauri870]

Now with the groundwork for the hybrid agent done in #5796 it is possible to have a yaml config file with both beats and otel configuration, for example:

hybrid-agent-config.yml

filebeat.inputs:
  - type: filestream
    id: filestream-filebeat
    enabled: true
    paths:
      - /tmp/filebeat.log
output.elasticsearch:
  hosts:
    - https://esendpoint
  api_key: api-key
  index: filebeat-index

---

receivers:
  filebeatreceiver:
    filebeat:
      inputs:
        - type: filestream
          id: filestream-fbreceiver
          enabled: true
          paths:
            - /tmp/fbreceiver.log
    output:
      otelconsumer:
    logging:
      level: info
      selectors:
        - '*'
    path.home: /tmp
    queue.mem.flush.timeout: 0s
exporters:
  elasticsearch/log:
    endpoints:
      - https://esendpoint
    api_key: api-key
    logs_index: fbreceiver-index
    batcher:
      enabled: true
      flush_timeout: 1s
    mapping:
      mode: bodymap
service:
  pipelines:
    logs:
      receivers:
        - filebeatreceiver
      exporters:
        - elasticsearch/log

When validating this file, we need to remove any top-level Beats-specific configuration to ensure that only the OpenTelemetry-specific components are validated.

[elasticmachine]

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