Add mime.types to docker container to select charset properly (#547)

* Add charset to content type in getHandler

Add charset to content type in the getHandler function to fix CJK-letter related issues.
If the content type is empty after trimming, set it to "text/plain; charset=utf-8".

* Add mailcap and mime.types to transfer.sh container

This commit includes /etc/mime.types file to the container, which is necessary to properly select the charset using MIME typing during file upload.

For more information, read https://github.com/dutchcoders/transfer.sh/pull/545#issuecomment-1528712181



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Co-authored-by: Andrea Spacca <andrea.spacca@gmail.com>