When a container has been deleted, HA-Dockermon needs to send an unavailable status back to Home Assistant.

Currently the switch is still marked as active, but the switch may remain as on or off depending on the last state stored in MQTT before the container was deleted.

When a message is sent to turn the container on/off, if Docker responds that the container doesn't exist, send back to Home Assistant Unavailable which will allow the Home Assistant user to delete or keep the entity if required.

Might need a way to explore the active MQTT topics so HA-Dockermon knows which entities it has previously created, and can then use that as a way to report updated status for all the containers when one eventually gets deleted.