Import: Index original filenames of related files

[natiz]

When uploading multiple related/stackable files, the non-primary files are missing the Original Name attribute. This PR ensures they are also assigned with their original file name.

Acceptance Criteria:

• Features and improvements are fully implemented so that they can be released at any time without additional work
• Automated unit and/or acceptance tests have been added to ensure the changes work as expected and to reduce repetitive manual work
• User interface changes are fully responsive and have been tested on all major browsers and various devices
• Database-related changes are compatible with SQLite and MariaDB
• Translations have been / will be updated (specify if needed)
• Documentation has been / will be updated (specify if needed)
• Contributor License Agreement (CLA) has been signed

[CLAassistant]

All committers have signed the CLA.

[graciousgrey]

Thank you for your contribution!

Because we want to create the best possible product for our users, we have a set of guidelines which ensure that all source code contributions are acceptable:

• The feature must be fully implemented
• Unit and acceptance tests have to be written
• The feature must work with sqlite and mysql
• The UI must be fully responsive
• It needs to be tested on multiple browsers and devices
• Translations need to be created for all languages
• Docs need to be updated

Reviewing, testing and finally merging pull requests consumes significant resources on our side. Unless it's just a small fix, it may take several months.

Thanks for your patience :)

[lastzero]

I will merge this improvement so it can be tested in our preview build. Thank you very much! 🥳

[lastzero]

I have started a new preview build for testing which should be available soon.