MCU Temp Usermod

This usermod adds the temperature readout to the Info tab and also publishes that over the topic mcutemp topic.

A shown temp of 53,33°C might indicate that the internal temp is not supported.

ESP8266 does not have a internal temp sensor

ESP32S2 seems to crash on reading the sensor -> disabled

Buildflag: -D USERMOD_MCUTEMP