Cannot include page headers and footers

I was looking into using spaCy Layout in a project I've been working on. I tested it out and noticed that the page headers and footers are not being included in the Document object.

I took a look through the source code and I see this is where the text spans are put together:
```python
for node, _ in document.iterate_items():
...
```
`iterate_items` iterates by default over only the Docling NodeItems in the "body" content layer. The page headers and footers seem to be in the other layer, "furniture", so they get excluded.

I understand that this makes sense to do for most NLP projects, but for ours we actually need those headers and footers. Could there be an option added to override this behavior?