Add e2e tests for oembed widget in page data form

The oembed widget only works on media entities per the \Drupal\media\Plugin\Field\FieldWidget\OEmbedWidget::isApplicablecode> method

I think we should remove it from the test module and then postpone this on 📌 Allow XB to be used on all node types Active

MR is for #2
This should move to Postponed once that is merged.

LGTM, verified this only applies to media entities.

Hope this convinces Wim now :)
Remember that if this is committed we need to mark it as posponed on 📌 Allow XB to be used on all node types Active

Talked to @penyaskito about this being postponed in #11: it's because we need to revisit this once XB supports media entities and not only xb_page and article Nodes. 👍

EDIT: lol, @larowlan already wrote that in #2 — my bad 🙈