Issue: 50313 - Add a NestedRole type to lib389
Add the NestedRole and the NestedRoles classes to src/lib389/lib389/idm/role.py
Add one test case that will test that the new class NestedRoles is
working fine.
https://pagure.io/389-ds-base/issue/50313
Reviewed by: Simon Pichugin, thierry bordaz