allow scaling based on gcs resources

https://github.com/google/kctf/blob/v1/kctf-operator/pkg/controller/challenge/volumes/persistentvolumeclaim.go#L14
https://github.com/google/kctf/blob/v1/kctf-operator/pkg/controller/challenge/volumes/persistentvolume.go#L25

I think we just need to define the capacity of the persistent volume accordingly to what we have in the node.

we would need to find a way to throttle access to the fuse fs somehow.

without it, it's possible for someone to spam the FS and make things slow for other tasks.