Ensure loadbalancing child exporters use the OTLP type so backend creation succeeds

[iblancasa]

Description

Link to tracking issue

Fixes #43950

Testing

Tested with config:

exporters:
  loadbalancing:
    retry_on_failure:
      enabled: true
      initial_interval: 5s
      max_interval: 30s
      max_elapsed_time: 60s
    sending_queue:
      enabled: true
      num_consumers: 10
      queue_size: 10000
      block_on_overflow: false
      sizer: items
    protocol:
      otlp:
        timeout: 1s
        tls:
          insecure: true
    resolver:
      dns:
        hostname: otel-receivers.test
        port: '4317'
        interval: 5s
        timeout: 1s

[l00py]

@iblancasa -- awesome quick turnaround time. Tested it and working as you expected.
One thing that I'm unsure is that the metrics will report twice, at loadbalancing and otlp. Any thoughts on that? :)
I can imagine this being valid in case where the end-user could use both the loadbalancing/otlp and otlp exporters. Seems like the loadbalancing/otlp will also be counted in otlp as well.

Here's an example:

loadbalancing

otelcol_exporter_sent_log_records_total{env="test",exporter="loadbalancing",exporter_host_name="otel-exporter",host_name="otel-exporter",instance="41ac214b-c822-4677-aa9d-f588e730dfdb",job="otel-exporter",server_port="8888",service_instance_id="41ac214b-c822-4677-aa9d-f588e730dfdb",service_name="otel-exporter",service_version="0.138.0-dev",team="observability",url_scheme="http",workload="exporter"}

otlp

otelcol_exporter_sent_log_records_total{env="test",exporter="otlp",exporter_host_name="otel-exporter",host_name="otel-exporter",instance="41ac214b-c822-4677-aa9d-f588e730dfdb",job="otel-exporter",server_port="8888",service_instance_id="41ac214b-c822-4677-aa9d-f588e730dfdb",service_name="otel-exporter",service_version="0.138.0-dev",team="observability",url_scheme="http",workload="exporter"}