a magnet based probe

This is a total reshape of Unklicky since microswitch is no longer used.
It is a compact design with just two sets of magnets, still providing sufficient stability.
It requires higher force for operating, so that it's possible to touch the z-endstop directly with the probe pin.

Unfortunately the Klicky parts are not compatible with this model.

BOM:
* 4x 6x2.6mm round magnet
* 1x 6x2.5(~3)mm hole 3mm, round magnet with hole
* 1x 3x2mm round magnet
* 1x M3x12 SHCS (carbon steel screw with strong magnetic required, partially threaded screw preferred)
* 1x M3x5x4mm heat set insert
* 2x M3x16 SHCS (for Stealthburner toolhead mount)
* 1x 6x3mm round magnet (for side dock)
* 2x M3x16 SHCS (for side dock)
* 2x M3x5x4mm heat set insert (for side dock)
* 1x M5x10 BHCS (for side dock mount)
* 1x M5x30 BHCS (for side dock mount)