Allow SylvaWorkloadCluster.spec.controlPlane and machineDeployments to be omitted

SylvaWorkloadCluster.spec.controlPlane and spec.machineDeployments are currently marked +required in the CRD, even though:

• Every field of ControlPlaneConfig (provider, replicas) is already optional, so users were forced to write controlPlane: {} to satisfy the requirement with no actual values.
• Making machineDeployments required, forced writing machineDeployments: {} for clusters with no worker machine deployments

We should make both SylvaWorkloadCluster.spec.controlPlane and spec.machineDeployment as optional fields