Updated MQTT docs (#2559)

* Updated MQTT docs
For dapr/components-contrib#1810

Signed-off-by: ItalyPaleAle <43508+ItalyPaleAle@users.noreply.github.com>

* Update setup-mqtt.md

Signed-off-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>

Co-authored-by: Mark Fussell <markfussell@gmail.com>

daprdocs/content/en/reference/components-reference/supported-pubsub/setup-mqtt.md

@@ -28,7 +28,7 @@ spec:
   - name: retain
     value: "false"
   - name: cleanSession
-    value: "true"
+    value: "false"
   - name: backOffMaxRetries
     value: "0"
 ```
@@ -43,9 +43,9 @@ The above example uses secrets as plain strings. It is recommended to use a secr
 |--------------------|:--------:|---------|---------|
 | url    | Y  | Address of the MQTT broker. Can be `secretKeyRef` to use a secret reference. <br> Use the **`tcp://`** URI scheme for non-TLS communication. <br> Use the **`ssl://`** URI scheme for TLS communication. | `"tcp://[username][:password]@host.domain[:port]"`
 | consumerID | N | The client ID used to connect to the MQTT broker. Defaults to the Dapr app ID. | `"myMqttClientApp"`
-| qos    | N  | Indicates the Quality of Service Level (QoS) of the message. Defaults to `0`. |`1`
+| qos    | N  | Indicates the Quality of Service Level (QoS) of the message ([more info](https://www.hivemq.com/blog/mqtt-essentials-part-6-mqtt-quality-of-service-levels/)). Defaults to `1`. |`0`, `1`, `2`
 | retain | N  | Defines whether the message is saved by the broker as the last known good value for a specified topic. Defaults to `"false"`.  | `"true"`, `"false"`
-| cleanSession | N | Sets the `clean_session` flag in the connection message to the MQTT broker if `"true"`. Defaults to `"true"`.  | `"true"`, `"false"`
+| cleanSession | N | Sets the `clean_session` flag in the connection message to the MQTT broker if `"true"` ([more info](http://www.steves-internet-guide.com/mqtt-clean-sessions-example/)). Defaults to `"false"`.  | `"true"`, `"false"`
 | caCert | Required for using TLS | Certificate Authority (CA) certificate in PEM format for verifying server TLS certificates. | `"-----BEGIN CERTIFICATE-----\n<base64-encoded DER>\n-----END CERTIFICATE-----"`
 | clientCert  | Required for using TLS | TLS client certificate in PEM format. Must be used with `clientKey`. | `"-----BEGIN CERTIFICATE-----\n<base64-encoded DER>\n-----END CERTIFICATE-----"`
 | clientKey | Required for using TLS | TLS client key in PEM format. Must be used with `clientCert`. Can be `secretKeyRef` to use a secret reference. | `"-----BEGIN RSA PRIVATE KEY-----\n<base64-encoded PKCS8>\n-----END RSA PRIVATE KEY-----"`
@@ -112,7 +112,7 @@ spec:
     - name: retain
       value: "false"
     - name: cleanSession
-      value: "false"
+      value: "true"
     - name: backoffMaxRetries
       value: "0"
 ```
@@ -121,6 +121,8 @@ spec:
 The above example uses secrets as plain strings. It is recommended to use a secret store for the secrets as described [here]({{< ref component-secrets.md >}}).
 {{% /alert %}}
 
+Note that in the case, the value of the consumer ID is random every time Dapr restarts, so we are setting `cleanSession` to true as well.
+
 ## Create a MQTT broker
 
 {{< tabs "Self-Hosted" "Kubernetes">}}
@@ -129,7 +131,7 @@ The above example uses secrets as plain strings. It is recommended to use a secr
 You can run a MQTT broker [locally using Docker](https://hub.docker.com/_/eclipse-mosquitto):
 
 ```bash
-docker run -d -p 1883:1883 -p 9001:9001 --name mqtt eclipse-mosquitto:1.6.9
+docker run -d -p 1883:1883 -p 9001:9001 --name mqtt eclipse-mosquitto:1.6
 ```
 
 You can then interact with the server using the client port: `mqtt://localhost:1883`
@@ -157,7 +159,7 @@ spec:
     spec:
       containers:
         - name: mqtt
-          image: eclipse-mosquitto:1.6.9
+          image: eclipse-mosquitto:1.6
           imagePullPolicy: IfNotPresent
           ports:
             - name: default