3KU optical end switch holder

An optical end switch holder for 3KU printer inspired by [design of Lars T.](https://plus.google.com/105737960853586562428/posts/f71oKPMMe7q)
The holder was tested with [this end switch](https://ru.aliexpress.com/item/1pcs-Optical-Endstop-Light-Control-Limit-Optical-Switch-for-3D-Printers-RAMPS-1-4-Free-Shipping/32436920427.html).
OpenSCAD sources are included.