[📖] the docs e2e test should run as part of CI

[wmertens]

Suggestion

We now have /e2e/docs-e2e which tests the docs, but it doesn't run automatically.

It should be run as part of CI if and after docs were built successfully.

Right now uses docs.dev, but it could also run preview; the client was already built.

[maiieul]

If we can we should run it both for docs.dev and docs.preview. Sometimes bugs can appear in one and not the other.