Attachment
constructor(fallback: String, color: String? = null, pretext: String? = null, text: String, authorName: String? = null, authorLink: Uri? = null, authorIcon: Uri? = null, title: String? = null, titleLink: Uri? = null, fields: List<AttachmentField>? = null, imageUrl: Uri? = null, thumbUrl: Uri? = null, footer: String? = null, footerIcon: String? = null, actions: List<PostAction>? = null)