Fix eslint and prettier

Fixes https://www.drupal.org/project/gitlab_templates/issues/3357971.

The eslint findings in keycdn are either legit or we havent configured eslint just right. I'm unsure. I copied block.js from Drupal core's block module and that's where the eslint findings are being reported.

In any case, this is an improvement over where eslint was so IMO we should merge.