fix(opentelemetry source): emit component_received_event* metrics when use_otlp_decoding is enabled

[thomasqueirozb]

Summary

Fixes missing component_received_events_total metric when use_otlp_decoding: true is enabled in the OpenTelemetry HTTP source.

The implementation of parse_with_deserializer now does the same thing that decode_metrics_body does when use_otlp_decoding is set to false. Now both functions are emitting metrics properly and in a similar manner.

Vector configuration

sources:
  open_telemetry_raw:
    grpc:
      address: 0.0.0.0:4320
    http:
      address: 0.0.0.0:4319
    type: opentelemetry
    use_otlp_decoding: true

How did you test this PR?

• Ran all existing OpenTelemetry tests (12 tests passed)
• Verified that http_headers_logs_use_otlp_decoding_true test now properly validates metric emission through assert_source_compliance

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the `no-changelog` label to this PR.

References

• Closes: Missing events count when switching to "use_otlp_decoding: true" #24316

[datadog-vectordotdev]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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