Suggestion: Add missing OTLP config steps for Rust instrumentation

[Snamnik]

We've successfully instrumented our Rust service using the official Datadog article on monitoring Rust with OpenTelemetry. However, it took us several hours to identify two important configuration steps that are not mentioned in the article, and we believe including them would help others avoid confusion:

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1. Enable OTLP Logs in the Datadog Agent

To ensure the Agent accepts logs over OTLP, the following environment variable must be set in the Agent configuration (as described here):

- name: DD_OTLP_CONFIG_LOGS_ENABLED
  value: "true"

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2. Configure OTLP Ingestion Mode (HTTP or gRPC)

To support either HTTP or gRPC ingestion for OTLP data, it's important to follow the configuration guide found in this Datadog doc.

otlp_config:
  receiver:
    protocols:
      grpc:
        endpoint: 0.0.0.0:4317

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It would be very helpful if these points could be added to the original article to make the Rust instrumentation process more seamless for future readers.

Thanks for the great work!