Add cypress test for 'show more' functionality

There has been [some discussion](https://github.com/guardian/dotcom-rendering/pull/5116/files#r919888387) about the Cypress test which was written as part of the [original 'show more' PR](https://github.com/guardian/dotcom-rendering/pull/5116/files).

Because this discussion ties into broader questions about how we should implement integration and visual regression tests for Fronts (and potentially other Layouts) it seems sensible to defer adding a Cypress test for show more until we've got more of a consensus on how to implement these types of tests more generally.

- [ ] Integration test for inserting and removing cards from an AJAX request.
- [ ] Percy snapshot?