[Feature Request]: Add RBAC capabilities to ManagementGroup module

[AlexanderSehr]

Description

Once the Bicep Issue is fixed, we should re-add the RBAC capabilities that were removed with issue #1542 .

As we introduced cross-module references, we might want to use the Management-Group RBAC module of the Authorization-RoleAssignments module.

[eriqua]

Ref also closed bug #1342

[rahalan]

needs to be tested again