Move cluster management api to operator handler

[yux0]

What changed? Move cluster management api to operator handler.

Why? The cluster management APIs are access by tctl which will depend on operator client later.

For describe cluster API, The operator handler depends on admin client DescribeCluster.

Option 2: Introduce a common component for describe cluster and have both admin handler and operator handler depends on the component.

How did you test it? Unit test

Potential risks

Is hotfix candidate?