test(node): Add integration test to demonstrate sample rate propagation of incoming trace

[Lms24]

While investigating an internally reported SDK issue, I had the suspicion that our Node SDK might handle the sample rate from an incoming baggage header incorrectly. Turns out that's not the case and things work correctly. I couldn't find a test though, where we specifically cover a non 1.0 sentry-sample_rate baggage value, so I figured there's value in adding this test.