Port Gutenberg's e2e tests to Core

[pento]

Issues like #45172 could've been avoided if we were running the e2e tests against Core.

For this to happen, we need:

• To get them running, of course.
• Some sort of stripped down Docker config, just for running the tests.
• A way to sync updates from the Gutenberg repo, which should probably only happen when we update the packages.

[pento]

Duplicate of #45165.