Add new pubsub_clients field in INFO (redis#2624)

Added in redis/redis#12849

Author: enjoy-binbin

commands/info.md

@@ -83,6 +83,7 @@ Here is the meaning of all fields in the **clients** section:
 * `blocked_clients`: Number of clients pending on a blocking call (`BLPOP`,
  `BRPOP`, `BRPOPLPUSH`, `BLMOVE`, `BZPOPMIN`, `BZPOPMAX`)
 * `tracking_clients`: Number of clients being tracked (`CLIENT TRACKING`)
+* `pubsub_clients`: Number of clients in pubsub mode (`SUBSCRIBE`, `PSUBSCRIBE`, `SSUBSCRIBE`). Added in Redis 8.0
 * `clients_in_timeout_table`: Number of clients in the clients timeout table
 * `total_blocking_keys`: Number of blocking keys. Added in Redis 7.2.
 * `total_blocking_keys_on_nokey`: Number of blocking keys that one or more clients that would like to be unblocked when the key is deleted. Added in Redis 7.2.