Back support panel

To provide more rear support for the shelf inserts in Natalie T's server rack from Printables (https://www.printables.com/model/1090551-modular-10-inch-server-rack-reworked/files), I adapted a standard 1U blank panel to fit between two shelf inserts. The adaptation involves adjustments to both height and depth for a better fit. If a shelf is equipped with, for example, power supplies, it can sag at the rear; this modification provides improved support. While one could theoretically add screws at the rear left and right, I also wanted a closure to conceal the internal components.