Improved filename verification of illegal characters when uploading a file

[RonnyB71]

Description

We had one occurence where a user somehow was able to upload a file with a colon (:) as part of the filename. We accepted this and stored the file in blobstore, but this caused issues further down the line when the service owner tried to download and process the file.

Additional Information

No response

Tasks

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Acceptance Criterias

• Given that a user tries to upload a file with illegal characters (:), when the app backend receives the request, then the app backend should reject the file and given the frontend a propper response identifying the problem