Clean Special Chars (e.g., &) from uploaded files (Lectures Attachments, File Upload exercises)

[sentry-io[bot]]

Sentry Issue: ARTEMIS-QQ6

InvalidPathException: Malformed input or input contains unmappable characters: /mnt/storage/uploads/attachments/attachment-unit/92/L06U01Antipatterndefinition&GoldenHammer.pdf
    at sun.nio.fs.UnixPath.encode(UnixPath.java:145)
    at sun.nio.fs.UnixPath.<init>(UnixPath.java:69)
    at sun.nio.fs.UnixFileSystem.getPath(UnixFileSystem.java:275)
    at java.nio.file.Path.of(Path.java:147)
    at java.nio.file.Paths.get(Paths.java:69)
...
(115 additional frame(s) were not displayed)

Internal Server Error

[jpbernius]

Reuse logic from file upload exercises: FileUploadSubmissionService.java#L176-L182