Add memtest86+ to (U)EFI-Only Linux Environments

Maybe you have been in the need to use a memtester like memtest86+. Maybe to test Ram-Overclocking (like XMP/DOCP), stability (like „more than 2 sticks of ram on AMD AM5“), because you suspect a faulty stick, or just as burn-in-test. Maybe you also realized, that memtest86+ – for the longest time – only supports booting in legacy CSM-Mode (aka. „legacy BIOS“). While this isn’t a big deal, when you have memtest on a bootable stick on a Board with CSM-Support (which is still true for most mainboards), it can be a challenge, when the Mainboard is (U)EFI-Only, when you try to add a boot-entry from a running Linux-System, or when having no physical access, like on Servers, when you are using the respective Out-Of-Band-Management-System. Or maybe, you just want to have memtest on hand, because you regularily have the need to run it for whatever reason.