This is an extremely useful addition to kiln-controller. I have been doing something similar for a couple of years. It is very easy to connect to a server such Adafruits or ThingsBoard and securely monitor your kilns from anywhere, I very much recommend this PR.

I adore this PR, I really hope it can be merged, but I do think it would be sensible to clean up this work to make sure it is very much feature specific. In this case I mean removing the changes to default values and the addition of the default config file. I actually very much like this idea and agree with some of the new default value suggestions, but I think to keep things clean, it would be best keeping such changes to a separate, future PR and ensuring the MQTT simply has a default value of not being enabled.

Additionally, I would love, love, love it if you could add an option for "Enabled Home Assistant Discovery" (again, false by default) that publishes the correct MQTT topics to ensure Home Assistant can automatically discover our Kiln and generate sensors and units etc. Though again, this could be another future PR by yourself or someone else (I can see myself doing it once your work is in:)