sensor: Add unique IDs to sensors

Home Assistant seems to lose data from MQTT sensors that do not have a
unique ID when it restarts.

src/thermostat/sensor.py

@@ -107,6 +107,7 @@ class Daemon:
     ):
         log.info("Successfully connected to MQTT broker")
         for key, value in SENSOR_CONFIG.items():
+            value["unique_id"] = f"sensor.{key}"
             client.publish(
                 f"homeassistant/sensor/{key}/config", json.dumps(value)
             )