added function to automatically remove MediaRecords without file every night

[ZombieAlienRobot]

Description of changes

Added a cronjob to check if mediarecords have a file and if not deletes them, every night at 3 am.

How has this been tested?

Please describe the test strategy you followed. If not tested, please explain why.

• [ ] automated unit test
• [ ] automated integration test
• [X] manual, exploratory test

Let it ran and delete MediaRecords.

Checklist before requesting a review

• [ ] My code is easy to understand
• [ ] My code follows the coding guidelines of this project
• [ ] My code fulfills all acceptance criteria
• [ ] The test coverage (line and branch) is reasonably high, especially on Service classes and other classes with complex logic
• [ ] I have made corresponding changes to the documentation or the wiki/adr
• [ ] I made no breaking changes in the database schema or if so, I will perform a database migration

Checklist for reviewer

• The code is easy to understand
• The code follows the coding guidelines of this project
• The code is tested or if not, the reason is documented or discussed
• The added and existing tests reasonably cover the code change
• The code has no breaking changes in the database schema or if so, the assignee is aware of it and will perform a database migration

[PaulBredl]

I would update the readme with the new property