Uploads a channel banner image to YouTube. The image must be a JPEG or PNG. The maximum file size is 6 MB. This returns a URL that you can then use with `update_channel` (if implemented) or through the standard API to set the channel banner.
Examples
if (FALSE) { # \dontrun{
# Set API token via yt_oauth() first
banner <- insert_channel_banner(file = "banner.jpg")
print(banner$content$url)
} # }