chore: Add release note for AppSync trace context extraction

Signed-off-by: David Ogbureke <david.ogbureke@datadoghq.com>

Author: Dogbu-cyber

releasenotes/notes/apm-appsync-trace-context-extraction-f4973d99cfdf3174.yaml

@@ -0,0 +1,7 @@
+---
+enhancements:
+  - |
+    APM: Add automatic trace context extraction from event.request.headers for
+    AppSync integration scenarios. This eliminates the need for customers to use
+    customized extractors for RUM → AppSync → Lambda resolver flows where
+    RUM-injected trace context is nested under event["request"]["headers"].