Stores a file with the specified base64-encoded contents inside the media folder. Alternatively you can specify a
absolute file path, or a url from where the file shell be downloaded. If more than one of `data`, `path` and `url` are provided, the `data` field will be used first, then `path`, and finally `url`. To prevent Anki from removing files not used by any cards (e.g. for configuration files), prefix the filename with an underscore. These files are still synchronized to AnkiWeb.
Any existing file with the same name is deleted by default. Set `deleteExisting` to false to prevent that
by [letting Anki give the new file a non-conflicting name](https://github.com/ankitects/anki/blob/aeba725d3ea9628c73300648f748140db3fdd5ed/rslib/src/media/files.rs#L194).