Add Dave Syer to Authors

Much of the content from architecture is borrowed, with permission
from Dave.

Issueh gh-7955

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
+Ben Alex; Luke Taylor; Rob Winch; Gunnar Hillert; Joe Grandja; Jay Bryant; Eddú Meléndez; Josh Cummings; Dave Syer
 :include-dir: _includes
 :security-api-url: https://docs.spring.io/spring-security/site/docs/current/api/
 :source-indent: 0