Add possibility to drag structured elements within the element selector modal

[Wiejeben]

Hello there!

When creating a new element via the element selector modal we noticed that it wasn't possible to assign a parent to an element within a structure. This is kind of understandable since this would open up a second element selector modal which might make things a bit messy but even after creating the element it couldn't be moved around.

The order by selector on the top right was set to "Structure", it does clearly show the hierarchy.

[Wiejeben]

Or else to prevent confusion maybe add the ability to disable the creation of new entries all together #9030.