Support Move Container Items for Experience Pages

This issue is part of CMS-13299 but since it has some specific choices, it has a separate issue to track history reasons better:

When editing an Experience Page in the CM, you can typically drag component items between components or reshuffling them within the same container. Within a container there is little room for confusion. Dragging between containers which belong explicitly to the XPage also is straight forward what to expect.

However, drag dropping them between containers where one container is an explicit container of the Experience Page and the other Container is of an inherited HST Configuration part, then it becomes complex and confusing

1. What if the cms user does not have the right role to modify the HST config part?
2. As a result of the action, the Experience Page document would change AS WELL AS the HST configuration : then if the Experience Page document gets published but the HST config not yet, the container item might be duplicate for some time or totally missing for some time (depending on whether moved to or from the XPage)

For the above reasons, we cannot otherwise than prohibit moving container items between an XPage and HST Configuration.

This has a backend impact as well as that it should also be correctly visualized within the frontend (container items can only be moved within either HST configuration OR within the Xpage, not between it). This issue is only for the Backend, a separate issue will be created for the frontend: the reason is that we first need to iron out how we want the frontend to behave exactly. See CMS-13326