Added release notes for 4.6.0

Author: Boy Baukema

docs/release_notes/4.6.0.md

@@ -0,0 +1,9 @@
+# OpenConext EngineBlock v4.6.0 Release Notes #
+
+Logging enhancements and removed outbound response caching.
+
+* [Improve logging performed during single sign-on](https://www.pivotaltracker.com/n/projects/1327084/stories/93698802)
+* [Log raw SAML HTTP requests when additional logging is requested](https://www.pivotaltracker.com/n/projects/1327084/stories/93698682)
+* [Research logging efficacy after various types of PHP errors and exceptions](https://www.pivotaltracker.com/n/projects/1327084/stories/93794322)
+* [Reconcile "system log" and "session log"](Reconcile "system log" and "session log")
+* [EB 4.4 reissues cached responses on Authn requests from any SP #179](https://github.com/OpenConext/OpenConext-engineblock/issues/179)