Provide a feature for side by side comparison of PDF and Converted markdown/json

[vishnoianil]

This feature can be helpful for user to review the converted PDF and ensure that the conversion is as expected. This will allow user to edit the markdown as well if requires.

We can explore (docling-ts)[https://github.com/DS4SD/docling-ts] for the possible integration here.

[jehlum11]

Overview:
We need to provide users to visualize, evaluate, and edit their converted input documents very easily in the UI.
Goals:
Users can compare the input document and the rendered converted document side-by-side.
They can easily fix various elements in the converted document like paragraphs, headings, tables, etc and ensure the final doc is updated.
Background:
Using docling serve to render the docling json format document, we can provide users a more intuitive experience than having them edit markdown files.