Export UsernameAttributes enum (#5197)

This change makes it possible to specify the usernameAttribute prop in TypeScript without using `any`.

Co-authored-by: Manuel Iglesias <6154160+manueliglesias@users.noreply.github.com>

packages/aws-amplify-react/src/Auth/index.tsx

@@ -34,6 +34,7 @@ export { default as TOTPSetup } from './TOTPSetup';
 export { default as Loading } from './Loading';
 
 export * from './Provider';
+export * from './common/types';
 
 export function withAuthenticator(
 	Comp,