MergeChildMapToParentMap merges child map of generic type map into parent map of generic type and returns merged mapping, if parentMap is nil then nil is returned.

LabelMatchingRegex is the official k8s label matching regex, pls refer https://github.com/kubernetes/apimachinery/blob/bfd2aff97e594f6aad77acbe2cbbe190acc93cbc/pkg/util/validation/validation.go#L167.

DeploymentEventHandler is not being used, TODO: find reason for creation and then remove.