MULE-6768 - making mule event transient in Authentication to avoid serializing the event during session serialization
(cherry picked from commit c644b9c712f318a9feb05a2413b7d13f21292bdc)

Conflicts:
	core/src/main/java/org/mule/security/DefaultMuleAuthentication.java
	core/src/main/java/org/mule/transport/AbstractMessageReceiver.java
	modules/jaas/src/main/java/org/mule/module/jaas/JaasAuthentication.java
	modules/pgp/src/main/java/org/mule/module/pgp/PGPAuthentication.java
	modules/spring-security/src/main/java/org/mule/module/spring/security/SpringAuthenticationAdapter.java
	modules/spring-security/src/test/resources/http-filter-test.xml