Add integration tests for discussion

As part of:
* https://github.com/guardian/dotcom-rendering/issues/10056

we're lifting up state in Discussion. This has as a result some interactivity to get lost from stories as we're stubbing state setter methods. (e.g. https://github.com/guardian/dotcom-rendering/pull/10311/files#r1465387059). This ticket is to track the interactivity we might want to test by adding integration tests in the future.

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