Allow to process password protected documents

[dolfim-ibm]

Current behavior with a password-protected file:

python -m docling_parse.visualize -c line -i myfile.pdf
2025-03-06 08:05:20,916 - INFO - page_boundary: crop_box
/private/tmp/parse/.venv/lib/python3.12/site-packages/docling_parse/visualize.py:133: UserWarning: This API is currently experimental and may change in upcoming versions without notice.
  parser = DoclingPdfParser(loglevel=log_level)
2025-03-06 08:05:20.938 (   0.027s) [         36D1512]             document.h:170    ERR| filename: myfile,pdf can not be processed by qpdf: myfile.pdf: invalid password

We should allow the possibility to specify the password in the docling-parse api.

Refs: DS4SD/docling#1081