Add the ability to download raw file, needed when size > 1MB

[genintho]

API DOC https://docs.github.com/en/rest/repos/contents

The API call to return the content of a file return an empty content if a file is bigger than 1MB. To be able to download that file, we need to provide the header application/vnd.github.VERSION.raw. When doing so, the API return a the raw file, instead of a JSON object with some attributes + the file content.

Because the API has a different behavior, I preferred to create a dedicated method as opposed to provide accept more option in the download method and having a bunch of if/else.

Note: a 3rd behavior exists for that API call when downloading markdown and passing the application/vnd.github.VERSION.html header, which is not supported by this code change.