[Features] support heterogeneous component configuration for ClusterSpec.Shardings API

[starnop]

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Scenario one, takes the specified pod instance offline, and the offline instance should be recorded in the component configuration of the corresponding shard.

Scenario two, horizontal scale up some instances for a shard due to traffic imbalance

Scenario three, vertical scale up some instances for a shard due to traffic imbalance

Scenario four, instance replacement requires scaling up before scaling down.

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