Update SDK spec to the latest W3C Baggage spec version (#2670)

* Update SDK spec to the latest W3C Baggage spec version

* Add changelog entry for #2670

* Fix location of #2670 in the changelog

Co-authored-by: Yuri Shkuro <yurishkuro@users.noreply.github.com>

CHANGELOG.md

@@ -29,6 +29,9 @@ release.
 
 ### Resource
 
+- Update the version of the W3C Baggage specification used for `OTEL_RESOURCE_ATTRIBUTES`.
+  ([#2670](https://github.com/open-telemetry/opentelemetry-specification/pull/2670))
+
 ### Semantic Conventions
 
 - Add `net.app.protocol.*` attributes

specification/resource/sdk.md

@@ -137,9 +137,10 @@ has higher priority.
 
 The `OTEL_RESOURCE_ATTRIBUTES` environment variable will contain of a list of
 key value pairs, and these are expected to be represented in a format matching
-to the [W3C Baggage](https://github.com/w3c/baggage/blob/fdc7a5c4f4a31ba2a36717541055e551c2b032e4/baggage/HTTP_HEADER_FORMAT.md#header-content),
-except that additional semi-colon delimited metadata is not supported, i.e.:
-`key1=value1,key2=value2`. All attribute values MUST be considered strings.
+to the [W3C Baggage](https://w3c.github.io/baggage), except that additional
+semi-colon delimited metadata is not supported, i.e.: `key1=value1,key2=value2`.
+All attribute values MUST be considered strings and characters outside the
+`baggage-octet` range MUST be percent-encoded.
 
 ## Resource operations