[feature request]add a controller in yurt-manager component for managing address of leader Yurthub and leader election configurations.

[rambohe-ch]

What would you like to be added:
Leader election configurations(like interConnectivity and poolScopeMetadata) and address of leader Yurthub is managed in the NodePool, but NodePool metadata is changed frequently because of status change. so if Yurthub on edge nodes get these information through list/watch NodePool, it will cause large network traffic between cloud-edge. moreover, These information can not be shared in the nodepool and each Yurthub should get this information from cloud kube-apiserver directly.

so we want to define Endpoints to manage these information, and all Yurthub only need list/watch this specified Endpoints resource to resolve these information about leader election configuration and address of leader yurthub.

• Input for controller: NodePool
• Output for controller: Endpoints
  1. each NodePool has a related Endpoints metadata, the name of Endpoints is: leader-hub-{nodepool-name}
  2. NodePool.Spec.InterConnectivity/NodePool.Spec.PoolScopeMetadata are stored in the Endpoints annotation
  3. NodePool.Status.LeaderEndpoints are store in the Endpoints.Subsets.

others
/kind feature

[rambohe-ch]

/assign @tnsimon