Another Ender 3 Pro PSU relocation

This is a remix of: https://www.thingiverse.com/thing:4101358 . It introduces the following changes to the design:
- fan is facing downward,
- increased tolerances,
- thinner end plates for less filament consumption,
- avoided collision of cable shroud with vertical aluminum extrusion,
- unfortunately the AC socket only fits mounted with the switch on the bottom.

Bolts that you will need:
- 4 M5x16 to screw into 40x40 extrusions (aluminum is soft, you don't need to tap it),
- 2 M4x10 for attaching psu to the holder (from the back),
- 1 M4x6 for attaching psu to the holder (from the top),
- rest can be reused from the stock PSu mount.

I used PLA, but any filament should do. A big nozzle (0.6mm or larger) is recommended.