Add missing type property on IAuthData (#2463)

Per spec, for example: https://spec.matrix.org/v1.2/client-server-api/#dummy-auth

Author: turt2live

src/interactive-auth.ts

@@ -44,6 +44,7 @@ export interface IStageStatus {
 
 export interface IAuthData {
     session?: string;
+    type?: string;
     completed?: string[];
     flows?: IFlow[];
     available_flows?: IFlow[];