allow federation-config as esm and sync/async exporting of config

[mchlbrnd]

This PR allows federation-config to be esm module that returns FederationConfig or sync/async function that returns FederationConfig. Use case includes to be able to add additional async logic before returning FederationConfig. for example:

import { withNativeFederation } from '@angular-architects/native-federation/config.js';

export default async function() {
  const config = await fetch('some-config-url');
  return withNativeFederation(config);
};