[#45896] Generate PDF document from a work package description

[as-op]

Please note: The work package is still in specification and the PR is a spike to find out about pain points.

• [x] Refactor for better resue
• [x] Reuse logo handling from PDF report
• [x] Use md-to-pdf to generate the document from a work package description
• [x] Trigger with entry in work package drop down menu
• [x] Hide behind feature flag generate_pdf_from_work_package

https://community.openproject.org/work_packages/45896