[BUG] Issue with file formats when meditation file is uploaded

[k-mlch]

Description:
An issue with file formats when the meditation file is uploaded

The issue was encountered when the added meditations were not working (the default meditations were working).

In the backend (backend/src/packages/files/files.service), in the 'create' function, when the 'fileKey' variable is created, it uses the second part of the ContentType (in this case, it would be 'mpeg'), but this is not correct.

According to this table, the '.mpeg' extension corresponds to a video format (video/mpeg). As a result, I get my files with the '.mpeg' extension in the db when they should actually be 'mp3'.