NEW_ATTACHMENT webhook payload
t() :: %MailSlurpAPI.Model.WebhookNewAttachmentPayload{ attachmentId: String.t() | nil, contentLength: integer() | nil, contentType: String.t() | nil, eventName: String.t() | nil, messageId: String.t() | nil, name: String.t() | nil, webhookId: String.t() | nil, webhookName: String.t() | nil }