Import the `dnf-json` Python script that is included in the "images" and
"osbuild-composer" repository into "osbuild".
`dnf-json` provides dependency solving capabilities by taking in some
JSON and then outputting the package set that JSON resolves to. Since it
is a Python script it moves into a subpackage of `osbuild`.
The script is renamed to `osbuild-depsolve-dnf`.
