don't use dnf --installroot with no /proc

In https://gitlab.com/redhat/rhel-primitives/containers/-/blob/a85fc4c9a0eb0a2d792d3176ca1f314dd0e56064/images/go/Containerfile#L5 we're doing a plain "dnf --installroot" into a target root without even /dev and /proc mounted. This is a very unfriendly thing to do for code being run in this environment. One can easily end up with weird stuff if e.g. some script blindly does foo >/dev/null and you end up with a regular file there.

However in the short term I'd say you should copy what is done in https://gitlab.com/fedora/bootc/base-images-experimental/-/blob/main/build/dnf-installroot which is a functional working example.

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