message: types(message): make attachment dimensions optional
  Reference:
diff: @@ -32,9 +32,9 @@ export interface Attachment {
  /** A proxied url of file */
  proxy_url: string;
  /** The height of file if an image */
  - height: number | null;
  + height?: number | null;
  /** The width of the file if an image */
  - width: number | null;
  + width?: number | null;
  }
  export interface Embed {
  