Go SDK: Propagate OTel context to Go SDK tasks

[viiccwen]

Closes #70165.

Go SDK tasks executed through the bundle gRPC path currently don't have the task instance's OpenTelemetry context carrier. This breaks trace continuity at the Go task boundary even though the protobuf schema already provides an otel_context field.

This change:

• forwards string-valued context-carrier entries through the existing bundle protobuf field.
• reconstructs the carrier when the bundle server receives the workload.
• extracts the W3C Trace Context into the task's context.Context, allowing task instrumentation and downstream API calls to inherit the remote parent.

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Was generative AI tooling used to co-author this PR?

• Yes - GPT-5.6 Sol

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[viiccwen]

cc @jason810496, @henry3260. 🙌