This PR removes the `isolatedConfig` option that has been deprecated
since v17. Back when it was deprecated, we had a migration to remove the
option and set `webpackConfig` with a generate config file that matches
the executor's built-in behavior. Now that we're removing the option, a
similar migration is added to generate the config files for any projects
that skipped the migration the first time.
e1b56f7c0a