refactor: replace free-disk-space with container-storage-action

[xynydev]

ublue-os/main#968
https://github.com/ublue-os/container-storage-action

Not sure how this works, but it's being adopted by ublue. From somewhere in the runner I guess a btrfs volume is mounted to work as storage for the container build.

[gmpinder]

This appears to be something that would only work with Podman builds

[HastD]

I think this is unnecessary now given #117.

[xynydev]

This appears to be something that would only work with Podman builds

If this is true, this is not something that can be implemented right now.

Maybe not unnecessary, though, as it doesn't require deletion of anything.