Add a new `cosa import` command that can be used to synthesize a cosa build from an already-built container image (which could've been built using podman/buildah/Konflux/etc...).

Then, it should look and feel mostly like any other cosa build, and one should be able to do e.g. `cosa buildextend-qemu` etc...

Import would:

• Download a container image in an oci.archive
• Create the build directory that contain the meta.json
• Populate what's is needed in meta.json to allow cosa build to work

Part of that logic is already in cosa build, we should probably look at splitting that logic.

How to test:

`cosa import quay.io/fedora/fedora-coreos:stable`
`cosa buildextend-qemu`

This should result in having a working fcos.qcow2 image built, we can run the kola test on that image.