Test PDF accessibility

While we have only three verified accessibility issues (ref. https://github.com/Altinn/app-lib-dotnet/issues/196) we should do another round of testing to ensure we meet the requirements.

The Authority for Universal Design of ICT have created guidelines that should be used as a reference when testing
https://www.uutilsynet.no/veiledning/pdf/218#kontroller_om_et_pdfdokument_er_universelt_utformet

In addition we should ensure:
* Correct use of heading levels allowing the user to navigate between elements
* Don't skip heading levels but follow the heading hierarchy
* Correct reading of the caption of a table, and avoud different "levels" in tables
* Good contrast
* Follow best practices for readability putting the answer below it's corresponding label

This issue is intended as a testing issue, any findings should result in new issues. The work done here should also result in a updated documentation on how to we do WCAG testing in relation with PDF creation.

Start with the Authority for Universal Design of ICT PDF guidelines linked in the issue and use them as the reference for the next accessibility-testing round. Check heading hierarchy, table captions and levels, contrast, and label-answer readability; record findings as separate issues and update the documentation describing WCAG testing for PDF creation.

Written by the indexing model from the issue text.