feat(otlp)!: Export OTLP spans with attribute-level OTel compatibility (#2091)

# What does this PR do?

This PR adds a configuration to the Trace Exporter to export spans with purely OpenTelemetry semantics. When enabled, this configuration updates the DD Span => OTLP Span mapping to exclude the following span tags from the output:
- `service.name`
- `operation.name`
- `resource.name`
- `span.type`
- `error.msg`
- `error.message`
- `span.kind`

This change also fixes the DD Span error message lookup to account for both the `error.msg` and `error.message` tag keys, since they are used interchangeably across Datadog SDKs.

# Motivation

We want to enable OpenTelemetry SDK users to migrate to the Datadog SDK in their language ecosystem, so this change allows them to export OTLP spans from the Datadog SDK without the shape of their data changing. This is most notable when using the OpenTelemetry Tracing API and OpenTelemetry Instrumentation Libraries to generate traces -- with this new semantic mode, the OTLP span should reach the backend without its semantics changing.

# Additional Notes

This may result in a breaking change since it affects the public function `libdd_trace_utils::otlp_encoder::map_traces_to_otlp`.

# How to test the change?

This is tested through unit tests in `libdd-trace-utils/src/otlp_encoder/mapper.rs` that validate the Datadog-specific attributes are excluded from the OTLP span.


Co-authored-by: zach.montoya <zach.montoya@datadoghq.com>

Author: zacharycmontoya

libdd-data-pipeline/src/otlp/config.rs

@@ -35,6 +35,10 @@ pub struct OtlpTraceConfig {
     /// Protocol (for future use; currently only HttpJson is supported).
     #[allow(dead_code)]
     pub(crate) protocol: OtlpProtocol,
+    /// When `true`, does not add DD-specific per-span attributes to the OTLP payload.
+    //  These attributes are: (`service.name`, `operation.name`, `resource.name`,
+    //  `span.type`, `error.msg`, `error.message`, `span.kind`)
+    pub otel_trace_semantics_enabled: bool,
 }
 
 /// Parsed OTLP trace-metrics exporter configuration.

libdd-data-pipeline/src/trace_exporter/builder.rs

@@ -330,7 +330,13 @@ impl TraceExporterBuilder {
         self
     }
 
-    /// Strip Datadog-specific `dd.*`/`_dd.*` data-point attributes from the exported histogram.
+    /// Enables OTel trace semantics, which does not add DD-specific per-span attributes
+    /// (`service.name`, `operation.name`, `resource.name`, `span.type`, `error.msg`,
+    ///  `error.message`, `span.kind`) to the OTLP payload.
+    /// Also strips Datadog-specific `dd.*`/`_dd.*` data-point attributes from the exported
+    /// histogram. This is useful when exporting to a native OTel backend that does not expect
+    /// Datadog semantics. The host language tracer is expected to observe this behavior by
+    /// setting the `DD_TRACE_OTEL_SEMANTICS_ENABLED` environment variable to `true`.
     pub fn enable_otel_trace_semantics(&mut self) -> &mut Self {
         self.otel_trace_semantics_enabled = true;
         self
@@ -488,6 +494,7 @@ impl TraceExporterBuilder {
             headers: build_otlp_header_map(self.otlp_headers),
             timeout: otlp_timeout,
             protocol: OtlpProtocol::HttpJson,
+            otel_trace_semantics_enabled: self.otel_trace_semantics_enabled,
         });
 
         let otlp_metrics_config = self.otlp_metrics_endpoint.map(|url| OtlpMetricsConfig {

libdd-data-pipeline/src/trace_exporter/mod.rs

@@ -566,7 +566,8 @@ impl<C: HttpClientCapability + SleepCapability + MaybeSend + Sync + 'static> Tra
             r.client_computed_stats = self.otlp_stats_enabled;
             r
         };
-        let request = map_traces_to_otlp(traces, &resource_info);
+        let request =
+            map_traces_to_otlp(traces, &resource_info, config.otel_trace_semantics_enabled);
         let json_body = serde_json::to_vec(&request).map_err(|e| {
             error!("OTLP JSON serialization error: {e}");
             TraceExporterError::Internal(InternalErrorKind::InvalidWorkerState(e.to_string()))