Add test document for reference parsing

[koppor]

This PR adds a test PDF for JabRef#10437

Idea:

1. Parse the attached PDF using the new feature
2. Compare the parse result with the .bib file

The .bib file can be modified (e.g., authors shortened, ...). I just wanted to provide a complete example and see how it goes.

Note that the referenes are very complete and maybe need to be shortened drastically.

I just wanted to start with something.

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

Update: I shortened the references to make them more "natural"

The references miss DOIs. In case parsing is much easier with DOIs, we can try to add them (maybe change some references in the example)

(More backround: https://tex.stackexchange.com/q/67444/9075)