`prepare` builds a multiarch image using qemu emulation. It turns
out that aarch64 emulation is slowest (due to emulating pointer
authentication) so it makes sense to run it on an aarch64 host. To do
that, we need only to adjust the check for qemu installation.
Unfortunately, docker arch names and Linux arch names are different,
so we have to add an ungainly translation, but otherwise it is a
simple loop.
The manifest manipulation commands stopped working with podman 3;
the containers-storage: prefix now throws errors.
Switch to `buildah manifest`; since we're building with buildah,
we might as well maintain the manifest with buildah as well.
Closes#8231
The current procedure for building images is complicated, as it
requires access to x86_64, aarch64, and s390x machines. Add an alternative
procedure that is fully automated, as it relies on emulation on a single
machine.
It is slow, but requires less attention.
Closes#8024
