Add an integration test for when the last moderator leaves

[nickvergessen]

Fix #4490

To check out it works, revert #4489 and run the test:

Without #4489

    Then user "participant2" gets room "room" with 404 (v3)               # FeatureContext::userGetsRoom()
      Failed asserting that 200 matches expected 404.
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    Then user "participant2" gets room "room" with 404 (v3)               # FeatureContext::userGetsRoom()
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