Alfawise BLTouch mount

Parametric BLTouch mount for Alfawise printers (U30, U30 Pro, U20).

Some parameters you can change when using Customizer/OpenSCAD:
* Thickness
* BLTouch cable side: left or right
* Cable pass slot diameter
* Nuts diameter and height
* Gaps between the mount and BLTouch/Printer parts

Marlin modifications:

#define X_PROBE_OFFSET_FROM_EXTRUDER -35 // X offset: -left +right [of the nozzle]
#define Y_PROBE_OFFSET_FROM_EXTRUDER -5 // Y offset: -front +behind [the nozzle]

Z offset is approximately -1.5 mm (mine is -1.42)