[o11y] Drop warning for exceptions reported with non-exception outcome

[fhanau]

This is actually the expected behavior in several cases and should not be a cause for concern:

• Non-exception outcomes other than OK may describe the ground truth more accurately than "exception", e.g. when exceededCpu is reported for an "exceeded CPU time limit" exception.
• A background task failure may lead to a canceled outcome – we should report the exception so the developer can understand what caused the cancellation.
• For some disconnects, we report OK outcomes to avoid noise but may still report exceptions caused by the disconnect like "Network connection lost" to indicate that the request actually disconnected.
• We may get exceptions from waitUntil tasks that finish running after a fetch request has already returned its response successfully – in that case it is only right to report an OK outcome since the fetch succeeded while still reporting the exception so that the developer is aware of the task failure.
• I was able to identify one case where this is genuinely an issue: This is being addressed in [o11y] Make sure that exceptions are reported for the right request in actors #7578.

This warning helped us identify some real-world issues, but at the end of the day the assumption that exceptions should only be reported when there's an exception outcome don't really reflect how worker requests behave in practice.

#7578 should land before this PR. Internal PR !15327 is also related but may actually increase the volume of this warning since it affects one of the benign cases, so it's probably better to land this first.

[ask-bonk]

LGTM!

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_{Reviewed commit: 02970b7d · github run}