Decrease clock speed of ESP32-C3 to 80 MHz to save power

[ypid]

The ESP32 family can be configured to different clock speeds or even at run time using the setCpuFrequencyMhz() call.

For more details refer to the Video from Andreas Spiess #410 Unknown ESP32 saving: Light Sleep, Clock Reduction, Modem Sleep, Hibernation, and a few tricks

I am using 80 MHz for a few months already with the I-9PSL-DE AirGradient ONE 9th Generation, see MallocArray/airgradient_esphome#130 for more details and experiments.

Things to watch out for when trying to lower the clock speed to 80 MHz:

• Less heat might make the temperature correction of the Open Air invalid.
• I don’t know if the Open Air Max might need the clock sleep of 160 MHz.