Use CE v3 and new login by default

with nuxtjs-drupal-ce 2.1.0 being released and integrated that part is done. we now need to optionally run

ddev composer require drupal/custom_elements:3.*@beta

But this is only work on the demo install, so nothing stopping us from tagging rc1!

adapted the project repo to add support for an optional CUSTOM_ELEMENTS_VERSION variable and set it via gitpod. With that we have now two login link versions, so I've update the project page with that. Default is 3.*@beta now.

Automatically closed - issue fixed for 2 weeks with no activity.