Cleanup Database regularly

[karjo24]

Is your feature request related to a problem? Please describe.
The database currently stores useless information. E.g. pinned courses that can no longer be accessed by the user remain in the database, because it has been set to a lower visibility setting, see (#1351). A more complete list of types of useless information should be produced before trying to implement this.

Describe the solution you'd like
Script that cleans up the database at regular intervals.

Describe alternatives you've considered
Leave as is.