make file path relative when creatig entry from pdf

[Arshadpd]

Closes #11173

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)
• [x] Manually tested changed features in running JabRef (always required)
• [ ] Screenshots added in PR description (for UI changes)
• [x] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [x] 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.

[Siedlerchr]

You can just push your changes, the PR will be updated automatically. No need to open close

[Arshadpd]

Thanks for the review @koppor ,

1. The spacing was actually reduced in efforts to remove the Checkstyle issues. It is rectified now.

2. I am trying to understand the comment on the "File" field, but if the concern is about the object " this.filePreferences = preferences.getFilePreferences(); want", I just wanted to let you know that I got the object name updated in one of the other commits to Jabref main branch, when I was syncing my fork. I also had to change my code to adapt the new object name for "FilePreferences".