feat(bigquery): add opentelemetry W3C Trace Context to headers

[ldetmer]

This adds header value using OpenTelemetry's W3C Trace Context Propagation.

[gemini-code-assist]

Summary of Changes

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This pull request enhances the observability of BigQuery operations by integrating OpenTelemetry's W3C Trace Context propagation. By injecting trace and span IDs into HTTP request headers, it enables seamless end-to-end distributed tracing, which is crucial for monitoring and debugging complex service interactions involving BigQuery.

Highlights

• OpenTelemetry W3C Trace Context Propagation: Implemented the propagation of OpenTelemetry W3C Trace Context into HTTP request headers for BigQuery telemetry, ensuring distributed traces are correctly linked across services.
• New Test Case for Trace Context: Added a dedicated test case to validate that the W3C traceparent header is correctly set with the active span's trace and span IDs during HTTP requests.

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[gemini-code-assist]

Code Review

This pull request implements W3C Trace Context propagation for HTTP requests within the HttpTracingRequestInitializer in the BigQuery telemetry module. This involves adding OpenTelemetry imports, injecting the trace context into outgoing HttpRequest headers, and a new unit test to verify this functionality. A review comment suggests an improvement to use a method reference (HttpHeaders::set) instead of a lambda for injecting the trace context, citing improved readability and adherence to the Google Java Style Guide.

[lqiu96]

IIUC, this is to ensure that the parent span's traceID and SpanID values are injected into the current span?

Or is this doing something different?

[ldetmer]

no, this is just adding the traceID/spanID into a standard opentelemetry header for tracking purposes. See requirement here. Using the library ensures it pulls the current span from context and creates it following the W3C standard for header label/format.