[pulsar-io] [doc] Add docs for Redis sink (apache#4046)

### Motivation

Add docs for Redis sink.

### Modifications

Add `io-redis.md`.

site2/docs/io-connectors.md

@@ -24,5 +24,6 @@ Pulsar Functions cluster.
 - [File Source Connector](io-file.md#source)
 - [Hdfs Sink Connector](io-hdfs.md#sink)
 - [MongoDB Sink Connector](io-mongo.md#sink)
+- [Redis Sink Connector](io-redis.md#sink)
 - [Solr Sink Connector](io-solr.md#sink)
 - [InfluxDB Sink Connector](io-influxdb.md#sink)

site2/docs/io-redis.md

@@ -0,0 +1,27 @@
+---
+id: io-redis
+title: redis Connector
+sidebar_label: redis Connector
+---
+
+## Sink
+
+The redis Sink Connector is used to pull messages from Pulsar topics and persist the messages
+to a redis database.
+
+## Sink Configuration Options
+
+| Name | Default | Required | Description |
+|------|---------|----------|-------------|
+| `redisHosts` | `null` | `true` | A comma separated list of Redis hosts to connect to. |
+| `redisPassword` | `null` | `false` | The password used to connect to Redis. |
+| `redisDatabase` | `0` | `true` | The Redis database to connect to. |
+| `clientMode` | `Standalone` | `false` | The client mode to use when interacting with the Redis cluster. Possible values [Standalone, Cluster]. |
+| `autoReconnect` | `true` | `false` | Flag to determine if the Redis client should automatically reconnect. |
+| `requestQueue` | `2147483647` | `false` | The maximum number of queued requests to Redis. |
+| `tcpNoDelay` | `false` | `false` | Flag to enable TCP no delay should be used. |
+| `keepAlive` | `false` | `false` | Flag to enable a keepalive to Redis. |
+| `connectTimeout` | `10000` | `false` | The amount of time in milliseconds to wait before timing out when connecting. |
+| `operationTimeout` | `10000` | `false` | The amount of time in milliseconds before an operation is marked as timed out. |
+| `batchTimeMs` | `1000` | `false` | The Redis operation time in milliseconds. |
+| `batchSize` | `1000` | `false` | The batch size of write to Redis database. |