Command topic should be exposed in 4.2 colab notebook

[sgbaird]

i.e., something like: neopixel_topic = f"sdl-demo/picow/{PICO_ID}/GPIO/28/"

Right now, neopixel_topic is embedded within mqtt_observe_sensor_data:

https://github.com/sparks-baird/self-driving-lab-demo/blob/c68ad0bc4c56a9222cfd7d3dc63c1ba89f203c9f/src/self_driving_lab_demo/utils/observe.py#L61

And should probably rename neopixel_topic to command_topic.

4.2 notebook: https://github.com/sparks-baird/self-driving-lab-demo/blob/main/notebooks/4.2-paho-mqtt-colab-sdl-demo-test.ipynb