Added automatic MQTT setup when firmware has login info inside local .env file

.env.example

@@ -0,0 +1,16 @@
+# Copy this file to `.env` and adjust the values before building.
+# The build system will inject these into the firmware without committing secrets.
+
+MQTT_DEFAULT_HOST=mqtt.example.com
+MQTT_DEFAULT_PORT=1883
+MQTT_DEFAULT_USERNAME=example-user
+MQTT_DEFAULT_PASSWORD=example-pass
+MQTT_DEFAULT_CLIENT_ID=example-client
+MQTT_DEFAULT_PUBLISH_TOPIC=amsreader/telemetry
+MQTT_DEFAULT_SUBSCRIBE_TOPIC=amsreader/command
+#MQTT_DEFAULT_SSL=true
+#MQTT_DEFAULT_PAYLOAD_FORMAT=0
+#MQTT_DEFAULT_STATE_UPDATE=false
+#MQTT_DEFAULT_STATE_UPDATE_INTERVAL=60
+#MQTT_DEFAULT_TIMEOUT=1000
+#MQTT_DEFAULT_KEEPALIVE=60