Multiple part cooling fans support. If find this useful, please comment the pull request: Klipper3d/klipper#6341
Configure the fan the same as a regular [fan].
One may define any number of sections with a "multi_fan" prefix.
The prefixless fan is active on startup.
ACTIVATE_FAN gcode command switches the fan that is used for cooling.
ACTIVATE_FAN FAN=fan_name Selects the active printer fan that reacts to
M106/M107 gcodes. Current fan speed is transferred over to the new fan.