Describe KKP user and admin privileges

We have to create a clear and appropriate table of the possible actions and privileges of a KKP user and admin somewhere over here in the docs: https://docs.kubermatic.com/kubermatic/main/architecture/role-based-access-control/

Start at the linked role-based access control documentation page and review the existing descriptions of KKP users and admins. Document the possible actions and privileges in a clear table, with separate coverage for each role; the work is done when the table accurately reflects the documented permissions.

Written by the indexing model from the issue text.