Add Eleftheria Stein to Reference Authors

Closes gh-9762

Author: rwinch

docs/manual/src/docs/asciidoc/index.adoc

@@ -1,5 +1,5 @@
 = Spring Security Reference
-Ben Alex; Luke Taylor; Rob Winch; Gunnar Hillert; Joe Grandja; Jay Bryant; Eddú Meléndez; Josh Cummings; Dave Syer
+Ben Alex; Luke Taylor; Rob Winch; Gunnar Hillert; Joe Grandja; Jay Bryant; Eddú Meléndez; Josh Cummings; Dave Syer; Eleftheria Stein
 :include-dir: _includes
 :security-api-url: https://docs.spring.io/spring-security/site/docs/current/api/
 :source-indent: 0