Antctl multi-cluster member token command enhancement

[luolanzone]

Describe what you are trying to solve
When the user is trying to initialize a multi-cluster ClusterSet, a member access token is required for member cluster to join leader cluster. For now, user can use antctl mc create membertoken or antctl mc init with --create-token option to create the member token. But there is no way via antctl to get the member token information again or delete created one.

Describe the solution you have in mind
Add antctl mc get membertoken and antctl mc delete membertoken sub-commands, so user can retrieve the token again, or delete the member token without involving kubectl.