Let's add here the image we'll be using for unencrypted confidential
tests. Later on, we'll make sure to build and use this image as part of
our CI.
The image can easily be built as a multi-arch image, and has `cpuid`
installed in case of `x86_64` build, so it can be used to detect whether
we're running on a TEE guest without having to rely on `dmesg | grep
...`.
Fixes: #7595
Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>
