camel-shiro: allow custom implementation of serialization

Serialization and deserialization of `ShiroSecurityToken` is used in this component. (see https://github.com/apache/camel/blob/master/components/camel-shiro/src/main/java/org/apache/camel/component/shiro/security/ShiroSecurityHelper.java#L36 and https://github.com/apache/camel/blob/master/components/camel-shiro/src/main/java/org/apache/camel/component/shiro/security/ShiroSecurityProcessor.java#L126)

Graal VM doesn't support `ObjectOutputStream.writeObject()` (see https://github.com/oracle/graal/issues/460). Which makes it impossible for camel-quarkus to make this component work in native (https://github.com/apache/camel-quarkus/issues/1844). There is a simple solution, to refactor serialization into a mechanism, which allows some kind of overriding.

(for example: Provide serialization interface. then quarkus could provide its own implementation)