The ObjectContent::to_file() function was not working properly,
as it could not write in a temporary file (created with tokio::fs::File::open(),
which opens a file in read-only mode).
To solve this issue, modified the way temporary files are opened to be
able to write inside of it.
* Add an example to download a file
This new example demonstrates how to download an object and store its
content into a file.
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Co-authored-by: Henk-Jan Lebbink <henkjan.lebbink@gmail.com>
Co-authored-by: Jean Sainctavit <jean.sainctavit@qarnot-computing.com>
