Add changelog for elastic#592 (elastic#805)

Author: basepi

CHANGELOG.asciidoc

@@ -23,6 +23,10 @@ endif::[]
 // Unreleased changes go here
 // When the next release happens, nest these changes under the "Python Agent version 5.x" heading
 
+[float]
+===== New features
+ * Added SERVICE_NODE_NAME config {pull}592[#592]
+
 [float]
 ===== Bug fixes
  * Fixed an issue with metrics collection raising RuntimeErrors {pull}802[#802]