chore(example): update otel trace example

[rosetta-livekit-bot]

Summary

• add a JS OpenTelemetry trace example that exports spans via OTLP/HTTP
• document generic OTLP configuration and Langfuse headers in the example
• include metrics logging and trace flushing on shutdown

Tests

• pnpm exec prettier --check examples/src/otel_trace.ts
• pnpm exec eslint examples/src/otel_trace.ts
• pnpm build

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Ported from livekit/agents#6178

Original PR description

make the otel trace example more generic (tested with langfuse)

[changeset-bot]

⚠️ No Changeset found

Latest commit: e657b85

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.