HostSpecSchema this helper function extracts the Host schema, so that it's made available for both workload domain and cluster creation.

SetExpansionOrContractionSpec sets ClusterExpansionSpec or ClusterContractionSpec to a provided ClusterUpdateSpec depending on weather hosts are being added or removed.

SetStretchOrUnstretchSpec sets ClusterStretchSpec or ClusterUnstretchSpec to a provided ClusterUpdateSpec depending on weather a witness host is being added or removed.

TryConvertToClusterSpec is a convenience method that converts a map[string]interface{} received from the Terraform SDK to an API struct, used in VCF API calls.