Don't force limits or resources when not pinning CPUs

[mflendrich]

Issue originally authored by tnozicka as #414

It's a common practice in Kubernetes to define only requests and no limits so the payload can grow with the dataset or number of users. Fixed limits prevent it. Unless we are pinning CPUs we should be user friendly and honor the ask. Also in kube resources are optional while our CRD has them required.

https://github.com/scylladb/scylla-operator/blob/master/pkg/api/v1/cluster_validation.go#L60-62