Symmetry Holder V4.0 for rear of Prusa printers

Updated the holder so that it can fit in the space between the power supply/logic board and the end of the frame. Not the most ideal solution as I'm not sure how torque is being applied here but it fits and supports the printer nicely.

The V1 file only works for the MK3(S+), the new ones work with either MK3 or MK4. The new files are also mirrored versions of each other so if you need to save 44kB of bandwidth downloading one and mirroring in the slicer works fine.