Option to set up mounts inside installroots

[evan-goode]

Currently, RPM scriptlets will fail inside installroots if they depend on common files and devices that are not present under the installroot, including:

• "virtual" devices in /dev (e.g. /dev/null, /dev/zero, /dev/urandom)
• /proc
• /tmp and /run

DNF could provide an option to automatically create these common directories and mount certain host paths inside the installroot, like https://gitlab.com/fedora/bootc/base-images-experimental/-/blob/main/build/dnf-installroot.

Inspired by discussion on https://matrix.to/#/#bootc:fedoraproject.org:

@cgwalters:

dnf doesn't do any container features with --installroot and punts that to higher level tools which isn't wrong, but also forces everything to wrap it in different ways. I crafted https://gitlab.com/fedora/bootc/base-images-experimental/-/blob/main/build/dnf-installroot which is a demonstration minimal version that works with as few as possible privileges inside a default podman/docker container

@supakeen:

The above dance is pretty much what every build tool has to do having a single approach to that is probably nice; e.g. I'd prefer dnf to be able to do the above itself.
There can however be a bunch more to it to make-things-work if one also wants to run things inside that root.