Add sharded Pub/Sub support for cluster

[supercaracal]

• https://redis.io/docs/interact/pubsub/#sharded-pubsub
  • Sharded Pub/Sub is only supported in cluster mode since version 7.
  • The channels are sharded by its name as same as keys.
  • Sharded Pub/Sub reduces consumptions of network bandwidth, on the other hand, global Pub/Sub consumes network bandwidth via cluster bus because all channel's messages are propagated to all nodes.
• https://redis.io/commands/?group=pubsub
  • Several commands replies cross-slot error if the client passes arguments of channels located multiple slots.
    • e.g. ssubscribe, sunsubscribe
• https://github.com/redis-rb/redis-cluster-client
  • The underlying library already supports sharded Pub/Sub but it's fixed some bugs recently.
• Adding support for Redis 7.0 commands #1187
• When will 5.0.8 be released? #1230