add id_token type (#202)

Author: giacomorebonato

types/index.d.ts

@@ -35,6 +35,7 @@ declare namespace fastifyOauth2 {
     token_type: 'bearer';
     access_token: string;
     refresh_token?: string;
+    id_token?: string;
     expires_in: number;
     expires_at: Date;
   }