Update What's New in 5.6

Author: jzheaux

docs/manual/src/docs/asciidoc/_includes/about/whats-new.adoc

@@ -6,6 +6,10 @@ Below are the highlights of the release.
 
 [[whats-new-servlet]]
 === Servlet
+* Core
+
+** Introduced https://github.com/spring-projects/spring-security/issues/10226[`SecurityContextChangedListener`]
+
 * Configuration
 
 ** Introduced https://github.com/spring-projects/spring-security/pull/9630[`AuthorizationManager`] for method security
@@ -14,6 +18,9 @@ Below are the highlights of the release.
 
 ** Added https://github.com/spring-projects/spring-security/pull/9483[SAML 2.0 Single Logout Support]
 ** Added https://github.com/spring-projects/spring-security/pull/10060[Saml2AuthenticationRequestRepository]
+** Added https://github.com/spring-projects/spring-security/issues/9486[`RelyingPartyRegistrationResolver`]
+** Improved ``Saml2LoginConfigurer``'s handling of https://github.com/spring-projects/spring-security/issues/10268[`Saml2AuthenticationTokenConverter`]
+
 
 * OAuth 2.0 Login