Is it possible to include external libraries in a twig template? I think I know the answer, because I tried to attach an external library like this:

{% set location = {'type': 'external'} %}
{{ attach_library('//example.com/example.js/v3/example.js', location) }}


This did not attach the desired library, am I missing something, or is this a non-starter?
Add external files in libraries: https://www.drupal.org/developing/api/8/assets

See the section on "CDN / externally hosted libraries".