Enhance oak-exercise for Principal base authorization

Since OAK-8190, a principal based authorization model has been added, which - among other things - allows creation of Immutable, non-JCR-resource-based ACEs. [0]

This issue is a request to enhance the existing Oak Exercise module [1] to illustrate these concepts and how the session with subject containing different principals operations in a repository (when the principals with different authorization models are combined).

[0] https://jackrabbit.apache.org/oak/docs/security/authorization/principalbased.html
[1] https://github.com/apache/jackrabbit-oak/tree/trunk/oak-exercise