This commit allows controlling the `osbuild --cache-max-size`
option. By default it will set the cache to 20GiB but allows
this to be controlled by the user.
Thanks to Simon for raising this.
Moves the files imported from `bootc-image-builder` directly under `pkg`
so they can be imported in reverse. Also fix up any import paths at the
same time.
Signed-off-by: Simon de Vlieger <supakeen@redhat.com>