Add demo data #33

[nuest]

Based on articles from the CODECHECK register: https://codecheck.org.uk/register/

• one article with two codecheckers
• three articles from three different codecheckers
• three articles from three different conferences/venues
• two articles from regular journals
• two institutional checks
• put them in one journal, but two issues

(there is some overlap between these criteria)

Use the same approach as here, but only use one PDF for the submissions (duplicate as part of a script, or duplicate locally and ignore copies): https://github.com/TIBHannover/geoMetadata/tree/main/testData