Feature/CloneSet supports hot-standy pods management

[yenniechen]

Ⅰ. Describe what this PR does

add feature that CloneSet supports hot-standby pods management

Ⅱ. Does this pull request fix one issue?

fixes #1762

Ⅲ. Describe how to verify it

1. ClonetSet CRD supports defining the desired hot-standby replicas in Spec and related replicas statistic in Status
2. CloneSet supports hot-standby management, such as:
   a. creating hot-standby pods while creating workload with the desired hot-standby replicas greater than 0.
   b. creating hot-standby pods while the desired hot-standby replicas increasing.
   c. inplace updating or recreating hot-standby pods while pod template changing.
   d. deleting hot-standby pods while hot-standby replicas decreasing
   e. deleting hot-standby pods while workload deleting.
   f. recovering hot-standby pods to normal firstly while scaling out and then creating hot-standby pods until its num equal to the desired hot-standby replicas.

Ⅳ. Special notes for reviews

[furykerry]

can you submit a kep first https://github.com/openkruise/kruise/tree/master/docs/proposals ?

[yenniechen]

can you submit a kep first https://github.com/openkruise/kruise/tree/master/docs/proposals ?

ok

[ABNER-1]

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