Pass HTTP request headers to docling when parsing via url

[lharrison13]

Requested feature

Might be out of scope but would it make sense to allow users to pass HTTP request headers to the DocumentParser and cli so we can parse documents on domains behind authentication?

Alternatives

Alternatively users can pull the document themselves then parse it, but I figured it would be nice to have OOTB.

[dolfim-ibm]

Actually, we have already the first steps for this feature. The code downloading the files allows for custom headers, see https://github.com/DS4SD/docling-core/blob/main/docling_core/utils/file.py#L52.

We only need to propagate the arguments all the way to the CLI and the main convert functions.

[lharrison13]

@dolfim-ibm I can try opening a pr to add this if you want. I think since you are the primary contact at IBM for DS4SD I technically need your permission to do so though.