Adding Baggage Span Tags docs (#29821)

* Adding Baggage Span Tags docs

* Update content/en/tracing/trace_collection/library_config/_index.md

Co-authored-by: Brett Blue <[email protected]>

* Update content/en/tracing/trace_collection/library_config/_index.md

Co-authored-by: Brett Blue <[email protected]>

* Update content/en/tracing/trace_collection/library_config/_index.md

Co-authored-by: Brett Blue <[email protected]>

* Update _index.md

* Update content/en/tracing/trace_collection/library_config/_index.md

Co-authored-by: Brett Blue <[email protected]>

* Update content/en/tracing/trace_collection/library_config/_index.md

Co-authored-by: Brett Blue <[email protected]>

* Update content/en/tracing/trace_collection/trace_context_propagation/_index.md

Co-authored-by: Brett Blue <[email protected]>

* Update content/en/tracing/trace_collection/library_config/_index.md

Co-authored-by: Brett Blue <[email protected]>

* Update _index.md

---------

Co-authored-by: Brett Blue <[email protected]>

Author: rachelyangdog

content/en/tracing/trace_collection/library_config/_index.md

@@ -221,6 +221,26 @@ The following configuration options behave consistently across the latest versio
   - `cf-connecting-ip`
   - `cf-connecting-ipv6`
 
+### Context propagation
+`DD_TRACE_BAGGAGE_MAX_ITEMS`
+: **Default**: `64` <br>
+**Supported Input**:  A positive integer <br>
+**Description**: The maximum number of key-value pairs in the baggage header.
+
+`DD_TRACE_BAGGAGE_MAX_BYTES`
+: **Default**: `8192` <br>
+**Supported Input**:  A positive integer <br>
+**Description**: The maximum number of bytes in the baggage header value. Values less than 3 bytes prevent propagation, because this is the minimum size for a valid key-value pair (for example, `k=v`).
+
+`DD_TRACE_BAGGAGE_TAG_KEYS`
+: **Default**: `user.id,session.id,account.id` <br>
+**Supported Input**:  A comma-separated string representing a list of case-sensitive baggage keys <br>
+**Caveats**: Not supported in Java, Ruby, Go, C++, and .NET <br>
+**Description**: A comma-separated list of baggage keys that are automatically applied as span tags to the local root span. For example, a baggage key `user.id` is tagged as `baggage.user.id` <br>
+This feature only applies to baggage extracted from incoming HTTP headers. Baggage set with the baggage API is not included.
+  - To tag all baggage items, set the value to `*`. Use this with caution to avoid exposing sensitive data in tags.
+  - To disable this feature, set the value to an empty string.
+
 
 [1]: /developers/community/libraries/#apm-tracing-client-libraries
 [2]: /tracing/trace_collection/compatibility/java/#framework-integrations-disabled-by-default

content/en/tracing/trace_collection/trace_context_propagation/_index.md

@@ -641,10 +641,13 @@ When the Datadog SDK is configured with the None format for extraction or inject
 
 ### Baggage
 
-_Currently available in Python, Ruby, PHP, Java, Node.js, C++, Go and .NET. For other languages, please reach out to [Support][11]_ 
-
 By default, Baggage is automatically propagated through a distributed request using OpenTelemetry's [W3C-compatible headers][10]. To disable baggage, set [DD_TRACE_PROPAGATION_STYLE][12] to `datadog,tracecontext`.
 
+#### Adding baggage as span tags
+_Available in Python, PHP, and Node.js. For other languages, reach out to [Support][11]_ 
+
+By default, `user.id,session.id,account.id` baggage keys are added as span tags. To customize this configuration, see [Context Propagation Configuration][13]. Specified baggage keys are automatically added as span tags `baggage.<key>` (for example, `baggage.user.id`).
+
 ## Further reading
 
 {{< partial name="whats-next/whats-next.html" >}}
@@ -661,3 +664,4 @@ By default, Baggage is automatically propagated through a distributed request us
 [10]: https://www.w3.org/TR/baggage/
 [11]: /help
 [12]: #customize-trace-context-propagation
+[13]: /tracing/trace_collection/library_config#context-propagation