File objects are unexpectedly closed after uploading to S3

[Finndersen]

It turns out that boto_client.upload_fileobj() causes a provided file handle/object to be closed after upload. This is an unexpected and undocumented behaviour, which just caused an error in production because the MemoryFileStore or LocalFileStore do not behave the same way.

This behaviour could be 'fixed' in S3FileStore.store_file() by using a workaround described here.

Alternatively, the MemoryFileStore and LocalFileStore should be updated to emulate this behaviour for local testing