Misc: Consider using symlink or hardlink to replace the need for file_ext parameter.

[inkhey]

Feature description and goals

Introduced here: #24 for tracim v2 support, the file_ext parameter permit to add extension separated from the filename. This is useful for filedepot file path as filedepot store file without extension.

This feature cause some issue as it create new case that also need to be tested.

To simplify things, it may be better to either:

• ask user to always specify extension and document how to use sym/hard link for this. (hard/symlink to be done outside of preview-generator)
• give both filename and mimetype, have some code that generated file_extension from mimetype which override the file_extension include in filename if needed and create a temporary sym/hardlink with the new filename to work on.

This permit to simplify the process.

It's unclear if symlink can work as expected. Hardlink seems more reliable for this but have some drawback too (weird result in du tool for example).