Export metadata to archived PDF/A properties

[Matthias84]

To make the inter-exchange with other tools more useful and to make use of the analyzed and assigned metadata of documents. If archived PDF/a documents would contain the contact, type, and tags information external workflows could use it. PDF properties as title, author, keywords are use by the most file explorers, search engines, ... .

This might result in a another run of the matcher, after the documents got OCR and rules were applied. We might make use of the pikepdf features, which is already a dependency of ocrmypdf.

Usecases are browsing, searching with Nextcloud or similar groupware, browse exported documents via file explorers on other users machines, ...