Admin user session management functionality

[ab-zackdemarco]

We have been using up until now our own forked copy of this code, and one thing we have noticed is that over time, the number of admin user sessions associated with the admin-cli client, is always increasing. After further investigation, there doesn't seem to be any code implementation that logs the admin user out when the KeycloakClient class is being disposed to help ensure that sessions are not being left live unnecessarily. (Our most recent instance of this was our dev keycloak instance had over 61K sessions being treated as live sessions for the admin-cli client.