This function is only available for composer plugins
This function is only available on context of type
function downloadComposerAttachment(attachmentId: string, cancelToken?: CancelToken): Promise<Link>;
This method will download the attachment specified for the composer's draft.
|String||The id of the attachment to be downloaded|
|CancelToken (optional)||Token to cancel the request|
The function returns a Promise that resolves with either a File containing the attachment data or undefined if it failed to fetch the attachment data.