Exclude current namespace instance from overlap warning

[jaredlockhart]

We added a warning that warns users if there are any live experiments/rollouts in existing namespaces because it could result in underenrollment. However this should only be the case where some experiment is allocated to namespace N and there are live experiments in namespace N-1. But it looks like we're also warning in the case where there are live experiments in namespace N, which isn't a problem. So we should update the logic to exclude live experiments in the same namespace instance.

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