Multiboard magnet holder

Remix of the Multiboard flat head bolt, small thread by including 3 magnet pockets for 6x2mm magnets (same ones required for Gridfinity). Works well for small metal objects like tweezers, pens and bed scrapper. The bolts will also perform their normal non magnet functions as per original design. Pause has been included in profile, just insert magnets and continue the print.