publish cache retained

src/pv_controller/MqttBase.py

@@ -69,5 +69,5 @@ class AbstractMqttPublisher(threading.Thread):
             logger.debug(f"mqtt message unchanged, not publishing: {topic} -> {payload}")
             return
         self.cache[topic] = payload
-        self.client.publish(topic, payload)
+        self.client.publish(topic, payload, retain=True)