Log serverless request receipt

[hansent]

Summary

Adds an early Request received log in the GCP serverless authorization middleware immediately after the existing observability context is prepared.

Why

Some model requests can crash or terminate the inference server before the normal access log is emitted. Because the existing access log is written after request handling completes, those crash-triggering requests can disappear from the logs entirely. Logging request receipt as soon as the serverless middleware sees the request gives us a durable breadcrumb with the route that was hit before any model loading or inference work begins.

Details

• Reuses the existing serverless observability setup instead of adding a separate outer middleware.
• Logs only when API_LOGGING_ENABLED is enabled.
• Includes method, path, request_id, and execution_id when available from _prepare_serverless_observability_context.
• Leaves the existing after-response structured access log unchanged.

Validation

• python -m py_compile inference/core/interfaces/http/http_api.py tests/inference/unit_tests/core/interfaces/http/test_http_api.py
• git diff --cached --check

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