[mqtt] publishMQTT Action accepts a bytearray payload (#12170)

* [mqtt] MQTT Action publishMQTT accept byte array

Signed-off-by: Jimmy Tanagra <jcode@tanagra.id.au>

bundles/org.openhab.binding.mqtt.generic/README.md

@@ -220,6 +220,7 @@ Once this action instance is retrieved, you can invoke the `publishMQTT(String t
 ```
 mqttActions.publishMQTT("mytopic","myvalue", true)
 ```
+Alternatively, `publishMQTT(String topic, byte[] value, Boolean retained)` can publish a byte array data.
 
 The retained argument is optional and if not supplied defaults to `false`.