add docs for db and redis

src/content/docs/modules/redis/client.mdx

@@ -0,0 +1,22 @@
+---
+title: Redis Client
+sidebar:
+    order: 1
+---
+
+The `redis.client` module connects to a Redis server. This module does not produce any messages and so using it as an `input` to a [route](/concepts/routes) would be pointless.
+
+- **type**: `redis.client`
+- **params**:
+    - **host**: the Redis server host
+    - **port**: the Redis server port
+
+### Example
+Connect to a Redis server running on `localhost` at port `6379`.
+```
+- id: redisClient
+  type: redis.client
+  params:
+    host: "localhost"
+    port: 6379
+```