Add Streamlit Docling concierge readme file and script

[sareegpt]

Description of the changes:

• Added a new streamlit-docling-concierge-readme-file.md that explains how to install and run the Streamlit UI for Docling.
• Added streamlit-docling-concierge.py, a Streamlit app script that allows users to upload or link to documents, apply Docling processing, and download results.
• The commit message uses Conventional Commits (feat: or docs:, etc.) to keep history clean.
• This concierge addition is not fully tested, and I am recommending Docling devs to finalize it for optimal flow. Note that my code was created with LLMs and reviews by experts is advised. You may contact me at sari/ at/ ibm dot com for questions.

Checklist:

• Documentation has been updated (the new README file serves as basic docs).
• Examples have been added, if necessary (the Streamlit script is an example in itself).
• Tests have been added, if necessary (not applicable, as this is primarily a UI script—no new library functionality).

[mergify]

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Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?(!)?:

[dolfim-ibm]

In the docling-serve project we have a gradio demo ui. It would be better to unify the efforts.

[cau-git]

@sareegpt We will close this PR since this work is very redundant to the official Gradio UI in docling-serve.