examples: Improve mqtt_relay to make individual and json topics optional

Add variables to control publishing individual topics and the json
topic.  Default both to on, so that there is no behavior change.

This eases use now, as one's local diff is cleaner.  It is also on the
path to reading these variables from a config file.

examples/rtl_433_mqtt_relay.py

@@ -35,6 +35,8 @@
 MQTT_PASSWORD = None
 MQTT_TLS = False
 MQTT_PREFIX = "sensor/rtl_433"
+MQTT_INDIVIDUAL_TOPICS = True
+MQTT_JSON_TOPIC = True
 
 def mqtt_connect(client, userdata, flags, rc):
     """Handle MQTT connection callback."""
@@ -76,22 +78,23 @@ def publish_sensor_to_mqtt(mqttc, data, line):
     elif "id" in data:
         path += "/" + str(data["id"])
 
-    # Publish some specific items on subtopics.
-    if "battery_ok" in data:
-        mqttc.publish(path + "/battery", data["battery_ok"])
+    if MQTT_INDIVIDUAL_TOPICS:
+        # Publish some specific items on subtopics.
+        if "battery_ok" in data:
+            mqttc.publish(path + "/battery", data["battery_ok"])
 
-    if "humidity" in data:
-        mqttc.publish(path + "/humidity", data["humidity"])
+        if "humidity" in data:
+            mqttc.publish(path + "/humidity", data["humidity"])
 
-    if "temperature_C" in data:
-        mqttc.publish(path + "/temperature", data["temperature_C"])
+        if "temperature_C" in data:
+            mqttc.publish(path + "/temperature", data["temperature_C"])
 
-    if "depth_cm" in data:
-        mqttc.publish(path + "/depth", data["depth_cm"])
-
-    # Publish the entire json string on the main topic.
-    mqttc.publish(path, line)
+        if "depth_cm" in data:
+            mqttc.publish(path + "/depth", data["depth_cm"])
 
+    if MQTT_JSON_TOPIC:
+        # Publish the entire json string on the main topic.
+        mqttc.publish(path, line)
 
 def parse_syslog(line):
     """Try to extract the payload from a syslog line."""