MMU2 Selector M1 with magnet

Problem: Sensor gets false reading because the sensor ball gets stuck on filament remains. You can see this by the red light on the sensor shows false reading.

Solution: add magnet to pull sensor ball down

Inspiration from:
https://www.thingiverse.com/thing:3264138?fbclid=IwAR3Br4l3gb8sW_vRHaejj-BtqOAKxJ_pdr-Z7ZXjYd72WMqB6pMG3DffwyQ

Basically the same as above, but with different magnets, and a different approach to get the magnet in. Based on the M1 version of prusa part.

Two vers