Create our own SessionCreationPolicy enum

Update `ManagementServerProperties` so that `security.sessions` no
longer uses `SessionCreationPolicy` from Spring Security. We now
use our own enun which allows `management.security.*` properties to
be set without the risk of a `ClassNotFoundException`.

Fixes gh-3888

spring-boot-samples/pom.xml

@@ -25,6 +25,7 @@
 		<module>spring-boot-sample-activemq</module>
 		<module>spring-boot-sample-actuator</module>
 		<module>spring-boot-sample-actuator-log4j2</module>
+		<module>spring-boot-sample-actuator-no-security</module>
 		<module>spring-boot-sample-actuator-noweb</module>
 		<module>spring-boot-sample-actuator-ui</module>
 		<module>spring-boot-sample-amqp</module>