Validate and improve where needed optimistic locking for CM interactions with HST Config components and XPage components

Methods like

ContainerItemComponentResource#createVariant
XPageContainerItemComponentResource#createVariant

have a 'versionStamp' as parameter which is used for optimistic locking. The response typically contains the updated versionStamp which can be used in the UI to update the versionStamp (optimistic locking value)

However, we need to check whether it still works correctly and see if we can align the implementation for it between XPageContainerItemComponentResource and ContainerItemComponentResource