Enable caching for the build pipeline

[ondrejbudai]

It seems like image-builder-cli doesn't enable any caching, see the output from ps:

/usr/bin/osbuild --store /var/cache/image-builder/store --output-directory fedora-41-qcow2-x86_64 - --export qcow2

Can we at least enable caching for the build pipeline with some reasonable default cache size (dunno, 20 GiB)? We can iterate from there. :)

[mvo5]

We will need osbuild/bootc-image-builder#812 as a prepreq I think.