Resolve "Docling-Modelle optional in das Image integrieren"

What is new and why?

Dieser MR fügt die Option hinzu, Docling-Modelle in das Parser-Image zu integrieren. Anpassungen in den Dockerfiles und der Dokumentation.

Related issues

Closes #52 (closed)

Author's TODOs

• if the licence_check-stage is not green: Download artefact (view in browser does not work for now) and check findings.json
• merged latest version of target branch (e.g., main or dev) into your branch
• check if SPDX identifier MPL-2.0 and Copyright-Text 2025 Land Baden-Württemberg <InnoLab@stm.bwl.de> exists in newly created and/or hasn't been deleted somehow in existing files
• adapted the readme
• Revised/new code parts have no # noqa directives
• Optional: Changelog adapted (further information)
• Optional: Update documentation files in /docs. Check if additional updates in the documentation at https://f13-os.de/ are needed.
• Optional: Update OpenAPI documentation whenever endpoints, API input classes, or API output classes change (see details)

Reviewer's TODOs

• Check if the Author did their checks well enough
• Tried out if the cause of the issue is solved as intended
• Check that code with old # noqa directives were revised
• Check that no new # noqa directives are included
• Optional: Changelog adapted (further information)
• Optional: Check if documentation files in /docs need to be updated. Check if additional updates in the documentation at https://f13-os.de/ are needed.

To keep in mind

• pre-commit used
• added logging output were necessary
• added/adjusted Errorhandling to avoid unwanted crashes and make proper debugging and testing possible
• Changelog has to be adapted before merging, at latest in the f13::inAbnahme step

CC @dymat und @dschury