feat: expose `depth` and `parentId` to `renderItemsContainer`

[paulrostorp]

This PR forwards the parentId prop and depth prop to renderItemsContainer.

My use case is that I need to render a text input at each level of the tree to allow creating values at that level. Having access to the depth prop allows me to render the input component at the proper level of indentation. The parentId is needed so I know where to push the new item :)

@lukasbach I cannot assign reviewers, but hopefully a mention is enough of a nudge 😄

[lukasbach]

Looks good, thanks for your contribution!