Supported options:
* _id (mixed): File document identifier. Defaults to a new ObjectId.
* aliases (array of strings): DEPRECATED An array of aliases.
Applications wishing to store aliases should add an aliases field to
the metadata document instead.
* chunkSizeBytes (integer): The chunk size in bytes. Defaults to
261120 (i.e. 255 KiB).
* contentType (string): DEPRECATED content type to be stored with the
file. This information should now be added to the metadata.
* metadata (document): User data for the "metadata" field of the files
collection document.