Add analog in to check temperature

[lpatiny]

It may be safer to read the temperature of the heating plate. This can be done with a thermistor

There is a good explanation here:

https://makersportal.com/blog/2019/1/15/arduino-thermistor-theory-calibration-and-experiment#:~:text=NTC%20thermistors%20are%20most%20common,resistance%20at%2025%20degrees%20Celsius.

We could place this on RX

MK3 with probe can easily be bought on aliexpress: https://www.aliexpress.com/item/32813575540.html?spm=a2g0o.placeorder.0.0.1aa2321eovjuh4&mp=1