Adding Baggage Span Tags docs

[rachelyangdog]

What does this PR do? What is the motivation?

• Adds DD_TRACE_BAGGAGE_TAG_KEYS in configuration docs and APM trace context propagation docs.
• Adds configuration for baggage limits including DD_TRACE_BAGGAGE_MAX_ITEMS and DD_TRACE_BAGGAGE_MAX_BYTES

Merge instructions

Merge readiness:

• Ready for merge

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Additional notes

[github-actions]

✅ Documentation Team Review

The documentation team has approved this pull request. Thank you for your contribution!

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/rachel.yang/baggage-span-tags-config/tracing/trace_collection/library_config/
• https://docs-staging.datadoghq.com/rachel.yang/baggage-span-tags-config/tracing/trace_collection/trace_context_propagation/

[brett0000FF]

Thanks for updating this content! I left a few minor edits.

[bm1549]

LGTM - thanks for keeping our docs up to date 🙌

[rachelyangdog]

/merge

[dd-devflow]

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2025-06-09 23:32:03 UTC ℹ️ Start processing command /merge

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2025-06-09 23:32:08 UTC ℹ️ MergeQueue: waiting for PR to be ready

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2025-06-09 23:32:51 UTC ⚠️ MergeQueue: This merge request was unqueued

[email protected] unqueued this merge request

[rachelyangdog]

/remove

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2025-06-09 23:32:47 UTC ℹ️ Start processing command /remove

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2025-06-09 23:32:49 UTC ℹ️ Devflow: /remove