create a mutatingWebhook as the adapter between clusternet obj and tke cluser obj

[huxiaoliang]

Problem:

The clusternet used cluster object is different from tke and tkestack, ManagedCluster in cluster is used to define the cluster managed by hub cluster, but tkestck/tke also have similar cluster obj but different spac, so it will cause compatibility issue and hard to integration.

Solution:

1. In order to consolidate them to support both user case, a mutatingWebhook get involved as the bridge to sync them, after that,
   both side only focus on individual business logic. With this loose-coupled design, the tke/tkestack still can use existing cluster object for create/list/query operation, clusternet focus on ManagedCluster register and status update.

2. The mutatingWebhook should designed as provider or plug-in mechanism so that support tke and tkestack case

3. sync status from ManagedCluster to tke and tkestack

• tkestack

root@vm-0-80-ubuntu:~/submariner-test# kubectl get cluster.platform.tkestack.io
NAME     CREATED AT
global   2021-06-17T08:07:05Z
root@vm-0-80-ubuntu:~/submariner-test# 

• clusternet

root@VM-0-56-ubuntu:~# kubectl get ManagedCluster.clusters.clusternet.io -n clusternet-fnbgq   
NAME                       CLUSTER-ID                             CLUSTER-TYPE                 KUBERNETES   READYZ   AGE
clusternet-cluster-gh7kt   fdcfbb35-e2f5-4327-b773-d39c60319822   EdgeClusterSelfProvisioned   v1.19.7      true     6d16h
root@VM-0-56-ubuntu:~# 

Reference:

• https://sruthakeerthi-k.medium.com/webhook-with-operator-sdk-4476bf1522ed