[BUG] Redis cluster does not automatically reshuffle slots when scaling in a shard.

[wangyelei]

Describe the bug
no reshard the slots

To Reproduce
Steps to reproduce the behavior:

1. kbcli kb install --version 1.0.0-beta.6
2. create cluster

apiVersion: apps.kubeblocks.io/v1
kind: Cluster
metadata:
  name: redis
spec:
  shardings:
  - name: shard
    shards: 3
    template:
      componentDef: redis-cluster-7-1.0.0-alpha.0
      disableExporter: true
      name: redis
      replicas: 2
      resources:
        limits:
          cpu: 500m
          memory: 512Mi
        requests:
          cpu: 500m
          memory: 512Mi
      serviceVersion: 7.2.4
      systemAccounts:
      - name: default
        passwordConfig:
          length: 10
          letterCase: MixedCases
          numDigits: 5
          numSymbols: 0
          seed: redis
      volumeClaimTemplates:
      - name: data
        spec:
          accessModes:
          - ReadWriteOnce
          resources:
            requests:
              storage: 20Gi
  terminationPolicy: Deletex

3. add shards to 4 than scale-in to 3